Meteorologist's Commentary

Turning warmer and more settled this weekend - 27th May 2021

After a notably chilly May so far, temperatures are on the rise this weekend reaching into the high teens and possibly low 20’s Celsius in places.

Daytime temperatures across Ireland have been below average so far this month, with many stations 2°C below the May average. However, as we head into the weekend, much of Ireland will enjoy a spell of settled and warmer weather to end the month.

Met Éireann meteorologist, Aoife Kealy said: “Whilst there’s some wet weather across southern & western areas today (Thursday 27th), northern and eastern areas will enjoy a largely dry and bright day, though rain will eventually move here later this afternoon and evening. This system will gradually clear through Friday, followed by high pressure becoming well established for the weekend.

“We’ll also have southerly winds which will bring warmer air and this, in combination with the strong sun at this time of year, means we’re going to see higher temperatures into the high teens and low twenties Celsius in places.”

The highest temperature reached so far this year is 21.2° Celsius, recorded on April 1st at Valentia, Kerry. With warmer weather in store this weekend we could see temperatures come close, especially on Sunday.

Surface pressure chart for Saturday 29th May showing high pressure across Ireland

Saturday will be generally cloudy to start with patchy drizzle mainly affecting some western areas and the northeast coast. Cloud will break up through the afternoon as sunny spells develop and it’ll become dry apart from isolated showers. Temperatures will reach around 16 to 19 Celsius, possibly 20 Celsius in the best of the sunshine across eastern areas.

Sunday will be another warm and largely dry day with sunny spells for many, temperatures reaching around 17 to 21 Celsius. The highest temperatures are expected in the midlands and east in the best of the sunshine, whereas areas further west and southwest will see cloudier skies and temperatures not quite as high.

UV levels will be moderate to high over the weekend, especially in strong sunshine. You can keep an eye on the UV index for your region here and remember to take care in the sun.

On Monday rain and drizzle will push east across the country, bringing a cooler and cloudier day with highs between 13 and 17 degrees. However, it should stay and warm dry for eastern and southeastern areas with sunny spells and temperatures reaching 18 or 19 degrees. Certainty then decreases as we move into next week but current indications suggest that it will stay warm with sunny spells, though showery rain will affect some areas at times also.

For the most accurate and up to date 7-day, hourly forecast for your local area on the Island of Ireland go to met.ie. The latest weather advisories and warnings for Ireland are on the Met Éireann Warnings page. These services and more are available on our free app – available from the App store for iPhone, and Play store for Android. Follow us on Twitter and Facebook for extra weather and climate content.

But whatever the weather please follow the public health advice and help keep everybody safe from COVID-19.

Weather for the Bank Holiday Weekend - 30 April 2021

A spell of unseasonably wet and windy weather is on the way this Bank Holiday Monday, as an active low-pressure system moves across Ireland.

Ahead of this system which will arrive in the early hours of Monday morning, Saturday and Sunday will see a mix of scattered showers and sunny spells, with temperatures below average for the time of year. An unstable northerly airmass extends across the country on Friday and Saturday, feeding in cold air and leading to some overnight frosts. On Saturday, slow-moving, scattered showers will develop through the afternoon and these could turn thundery at times along with the risk of hail. In between showers there will be good sunny spells with temperatures of 9 to 12 degrees Celsius expected. Most showers will ease through Saturday night with temperatures dipping under clear spells to around -1 to +3 degrees Celsius, leading to a frost in a few places along with mist patches.

Forecast airmass chart for Saturday 1st May showing the cold northerly airflow over Ireland. Blue colours indicate a cold airmass.

On Sunday a westerly airflow will establish across Ireland along with a slight ridge of high pressure, leading to a good deal of dry weather but still a few scattered showers could pop up in places – though these aren’t expected to be as heavy as Saturday. Temperatures on Sunday will still be on the cool side around 9 to 13 degrees Celsius, but it could feel quite pleasant in long sunny spells.

Commenting on the transition to more unsettled weather on Bank Holiday Monday, Met Éireann forecaster, Andrew Doran-Sherlock, said: “Later on Sunday night cloud will push in across the country, heralding a change to much more unsettled conditions as a low-pressure system makes its way towards Ireland from the Atlantic.”

“Monday will start wet and blustery across Ireland with unseasonably strong winds developing quite widely, along with the potential for gale or near gale force winds across coastal areas. There may also be a risk of localised flooding in areas expected to see the heaviest and most persistent rain, particularly across Atlantic and northern counties.”

Andrew continued: “The low-pressure system will clear eastwards away from Ireland later on Monday, with a northerly airflow re-establishing across Ireland. This will keep temperatures below average next week, around 8 to 12 degrees Celsius and it’ll stay on the unsettled side too.”

But whatever the weather please follow the public health advice and help keep everybody safe from COVID-19.

A cold weekend ahead

A spell of unseasonably cold weather is forecast across Ireland this weekend, with daytime temperatures well below average and some very cold nights and widespread frosts ahead.

Met Éireann meteorologist Emer Flood, said: “We’re seeing another spell of cold weather this weekend as an arctic airmass re-establishes across the country through Friday, bringing the chance of scattered wintry showers of sleet, hail and snow over the weekend. Temperatures today (Friday 9^th) will reach around 6 to 10 Celsius, followed by a very cold night with a widespread sharp frost as temperatures overnight fall to around -3 in places.

“Saturday will be another cold day with temperatures limited to around 5 to 9 Celsius, once again falling to around -3 in places overnight and another widespread frost with the risk of icy stretches.”

Forecast chart for Saturday 10th April showing a cold northerly airflow across Ireland (blue colours) that will bring below average temperatures, along with the chance of wintry showers of hail, sleet and snow.

Along with bright spells of sunshine over the weekend, the cold Arctic airmass will bring the chance of scattered wintry showers of sleet and hail, especially on Saturday. There’ll also be a risk of thunderstorms, as well as snow showers over the hills and mountains. Showers will be lighter and less widespread on Sunday.

Sharp frosts at this time of year can cause problems for gardeners, so take care to cover vulnerable plants and protect from frost damage. The cold weather can also pose challenges for farmers and so we’re encouraging farmers to keep an eye on our farming commentary.

Looking ahead to next week, meteorologist Emer Flood continued: “Later on Sunday conditions will turn less cold, as northerly winds are replaced by slightly milder westerly winds. Monday will be a cloudier day with rain spreading from the west to most areas during the day. Temperatures will be slightly up from the weekend too, with highs of around 7 to 10 Celsius.”

But whatever the weather please follow the public health advice and help keep everybody safe from COVID-19.

A tale of two halves this Easter Weekend

The weather in the lead up to Easter weekend will be largely dry and settled with sunny spells for most. However later on Easter Sunday we’ll see a big change as much colder air arrives across the country, introducing the chance of wintry showers of hail, sleet and snow.

Met Éireann meteorologist, Matthew Martin, said: “High pressure will establish across Ireland in the run up to Easter, allowing a spell of settled weather lasting until the first half of Easter Sunday.

“It’ll be largely dry with sunny spells for most, though there’ll be a bit of a temperature contrast – today and Good Friday we could see highs of around 15 to 18 Celsius across southern and western areas in the best of the sunshine, whereas northern and eastern areas will be notably cooler as easterly breezes keep temperatures at around 10 to 12 Celsius. These coastal areas may also see low cloud lingering through the first part of the day. Saturday will be another dry day with good spells of sunshine and temperatures of around 10 to 13 Celsius, still feeling cooler though along northern and eastern coasts.”

Commenting on the forecast for Easter Sunday and the change to colder conditions, Matthew continued: “Easter Sunday will start dry with sunshine for most and whilst southern areas will continue to enjoy a dry and bright day, a cold front will introduce cloud and rain across the northern half of the country through the afternoon – it’s this cold front that opens the gates to very cold air from the Arctic from Easter Sunday night and through much of next week.”

Forecast chart for Monday 5th April showing a colder, northerly airflow across Ireland (blue colours) that will bring wintry showers of hail, sleet and snow across the island.

The cold airmass will introduce the chance of wintry showers of hail, sleet and snow on Easter Monday and Easter Tuesday, with temperatures limited to around 3 to 7 Celsius. Temperatures overnight will widely fall close to freezing with a touch of frost in places, which could cause problems for gardeners so take care to cover vulnerable plants and protect from frost damage.

The cold snap could also pose challenges for farmers and so we’re encouraging farmers to keep an eye on our farming commentary ahead of the cold conditions arriving later this weekend.

But whatever the weather please follow the public health advice and help keep everybody safe from COVID-19.

Vigorous depression to bring severe winds with a cold and unsettled weather regime to follow

Update on Wednesday 10 March 15:00

A vigorous depression will track to the northwest of Ireland tonight with very strong south-westerly winds developing over Ireland, veering westerly overnight. Gales will develop around all Irish coasts with Storm Force winds expected for a time in south-western sea areas. Status Orange wind warnings are in operation for County Kerry and County Cork from 8pm today (Wednesday 11^th March) until midnight with a Status Yellow Weather Warning in operation for much of the rest of the country through until 7am Thursday 11 March. See full details on our weather warnings here: https://www.met.ie/warnings/today

(Fig 1: Position of depression at 00UTC 10 March, centred to the southwest of Ireland with a central pressure of 967hPa. The low pressure system will track to the northwest of Ireland tonight bringing a swathe of very strong winds across Ireland with some severe gusts in the south and southwest expected)

In the wake of the vigorous depression a cold and unstable westerly air-flow will follow over Ireland with showery conditions and brisk winds. There will be widespread showers on Thursday, Friday and Saturday with a risk of hail and some thunderstorms. A cold polar maritime air-mass will lie over Ireland and this will allow for some wintry showers over high ground, especially on Saturday.

(Fig 2: A cold and unstable westerly air-flow will become established over Ireland on Thursday 11 March with heavy showers embedded in the flow)

(Fig 3: Many of the showers that follow will be heavy with a risk of hail and lightning. The above chart shows the risk of lightning across Ireland on Thursday 1200UTC forecast by IREPS)

Early indications are that milder weather will begin to move in for Sunday and next week with some rain or showers with a trend for high pressure to become established near Ireland by the middle of next week allowing for drier and more pleasant weather conditions to develop.

(Fig 4: Early indications are that high pressure will build in over Ireland for St. Patrick’s Day but there is still some uncertainty in the forecast)

Monday 08 March 15:00

After a rather quiet start to meteorological spring, conditions will turn much more unsettled this week with spells of wet and very windy weather on the way.

High pressure has brought largely dry and settled weather since the start of March, but as the jet stream moves over Ireland in the next few days this will steer a succession of Atlantic low-pressure systems towards us.

Met Éireann meteorologist, Paul Downes, said: “Today (Monday 8^th) will be the last day of the current spell of settled weather, before conditions turn widely unsettled from tomorrow with spells of wet and windy weather expected through the rest of the week.

Image: Forecast chart for 1800UTC Wednesday 10th March showing deep low to the NW of Ireland

“Although tomorrow (Tuesday 9^th) will start dry, rain and strong winds will push east across the country from tomorrow afternoon, becoming widespread by early evening. Further wet and very windy weather is expected on Wednesday as a deep low-pressure system tracks to the northwest of Ireland – bringing very strong south-westerly winds and spells of heavy rain through Wednesday afternoon and Wednesday night.”

Met Éireann has issued a nationwide yellow wind warning from 12:00 on Wednesday, to 07:00 on Thursday, where mean wind speeds could reach 50 to 65 km/h and gusts could reach around 100km/h in exposed locations, with damaging impacts possible.

Meteorologist Paul Downes continued: “During the early hours of Thursday this low-pressure system will clear away from Ireland, introducing a colder and more unstable airmass. However, it will remain very windy into the weekend along with blustery showers, these possibly turning wintry over high ground.”

Image: Forecast chart for Friday 12th March showing cooler polar maritime airmass over UK & Ireland

But whatever the weather please follow the public health advice and help keep everybody safe from COVID-19.

Cold Snap Forecast Update – 8 February 2021

Updated by Matthew Martin on 08/02/2021

Monday-Wednesday: Risk of snow showers, frost and ice

A cold easterly air-flow has now become established over Ireland and over the next few days the risk of snow showers will increase with eastern counties at greatest risk. The risk of snow accumulations will increase tonight (Monday night), through tomorrow (Tuesday) and for a time on Wednesday before the main focus for snowfall risk turns to the attempted frontal breakdown from the Atlantic on Thursday and Friday.

Sea-effect snow showers

The risk of wintry showers over the next few days will be driven by what is termed the ‘sea-effect’. Similar to lake-effect snowfall that is common place in North America during winter, sea-effect snow is a term used to describe the mechanism by which showers develop over the sea during winter. Sea/Lake effect snow occurs when cold polar or arctic air flows over relatively warm water, generating convective bands of showers downwind from the body of water. These shower bands can at times become quite narrow and intense giving significant falls of snow in very localised areas whilst some adjacent areas receive very little snowfall. Convective snow showers or bands are enhanced by lift due to frictional convergence and orography over the leeward shore and other factors such as wind fetch play a critical role in determining the intensity and extent of the sea-effect snow showers or bands. In Ireland, the Irish Sea is often the origin for many of our wintry showers during an easterly or north-easterly air-flow, however, they can also form in northern sea areas and in the Celtic Sea.

Typically, the temperature difference between the water surface and the lower atmosphere (850hPa) must be at least 13°C to support convective sea-effect shower formation over the Irish Sea. At present sea-surface temperatures are around +8°C whilst forecast 850hPa temperatures are around -10°C, resulting in a 18°C differential which should be sufficient to create some snow showers over the coming days.

Fig 1: ECMWF Sea Surface Temperature forecast for Monday 00UTC February 8th 2021

Fig 2: ECMWF Forecast chart of 850hPa temperature for Monday 1200UTC February 8th 2021

Areas at greatest risk of seeing snowfall are highlighted in the white/green shades in the ECMWF forecast charts below. However, this is a rough guide and showers are likely to be more widespread than highlighted in these graphics.

Fig3: ECMWF Forecast snowfall risk Monday night to Wednesday

Thursday & Friday: Frontal snow risk

On Thursday, frontal rain-bands in the Atlantic are forecast to move towards Ireland and as they encounter the cold air in situ over Ireland further snowfall is predicted. However, there is some uncertainty as to how far these frontal bands track north-eastwards over Ireland as high pressure over Scandinavia is dominating and acting to weaken these fronts as they move into the cold air. However, current projections indicate a spell of sleet and snow spreading north-eastwards over Ireland on Thursday and into Friday bringing accumulations of snow to many areas. However, the snow may transition to rain in some southern and western parts as milder air attempts to move in from the Atlantic.

Fig 4: Forecast chart for Thursday 1200UTC 11 February 2021 shows low pressure in the Atlantic and high pressure positioned over Scandinavia. Over Ireland, there is a boundary between very cold air to the east and northeast and milder air from the Atlantic with a spell of snow expected

Fig 5: Forecast rain, sleet and snow on Thursday 0600-1200UTC 11 February 2021

Fig 6: Forecast rain, sleet and snow on Thursday 1800-2359UTC 11 February 2021

At time of writing, a weather advisory is currently in operation and weather warnings are likely to be issued in the coming days.

As always, you can stay up to date with Met Éireann’s weather and warnings by monitoring the following pages on our website and please sign up for weather warning notifications on your smartphone Met.ie app.

https://www.met.ie/forecasts/national-forecast

https://www.met.ie/warnings

By Meteorologist Liz Walsh, 4th Feb 2021

Our weather is expected to turn progressively colder from early on Sunday 7th February, with the cold spell now looking likely to last well into next week. The origin of the cold air over Scandinavia will bring a northeasterly or easterly component to the wind-flow over Ireland. That wind will be especially noticeable on Sunday and Monday with gusty east to northeast winds likely to produce a significant wind-chill factor.

00z Run ECMWF from 4th Feb.
Wet Bulb Potential Temperature forecast from Sunday 7th – Wednesday 10th February.
Indicates temperatures at around 1.5km (850hPa) up in the atmosphere. Below zero with precipitation = snow likely at surface.

Daytime temperatures are expected to struggle in the low single figures, generally 1 to 3 degrees Celsius, which means any frost or ice that forms at night will be slow to clear, if it clears at all, so the risk of icy roads and footpaths will increase.

ECMWF Forecast Daytime Maximum Temperatures on Sunday, Monday & Tuesday (l-r)

Snowfall is expected in the form of showers from Sunday onwards, but more especially later on Monday and during Tuesday. Any showers are likely to be restricted to eastern parts of Leinster and Ulster initially, but a few may push further inland during Tuesday.

Forecast snow for Midday Tuesday 9th Feb over 3 consecutive runs of the ECMWF model. Latest run on the left – earlier runs from Monday 3rd Feb on the right.

There is still a high degree of uncertainty in the forecast from Wednesday 10th February onwards, but it looks as though Atlantic frontal systems will attempt to push milder air in from the south to displace the cold air in situ over Ireland.

It is still too early to predict how energetic or vigorous these frontal systems will be, and that has a downstream effect on the impact that this clash of mild and cold air may have over Ireland. If the frontal feature is vigorous, for example, it would likely make quick progress northeastwards over the country and any associated snowfall would be a transient affair with rain following behind. However, if the frontal system has less energy as it comes towards us and starts to become slow-moving either on its approach or as it tracks over us, we could end up in a situation where some parts of Ireland could see more significant and lasting snowfall.

Whatever the case snow-ice and/or low temperature warnings are likely in the coming days for conditions from Sunday through Tuesday, and forecasts for the latter part of next week will be updated and fine-tuned as we move closer to the time.

As always, you can stay up to date with Met Éireann’s weather and warnings by monitoring the following pages on our website:

https://www.met.ie/forecasts/national-forecast

https://www.met.ie/warnings

But whatever the weather please follow the public health advice and help keep everybody safe from COVID-19.

Unsettled weekend ahead as the battle of warm and cold air poses multiple risk-29th Jan 2021

by Paul Downes, Meteorologist.

Wet and windy weather tonight, gradually getting colder Saturday with the risk of sleet and snow increasing.

Over the coming days Ireland will lie between colder air to the north and an active zonal Atlantic pattern to the south that will feed in several lows bringing rain sleet and snow at times as well as blustery east winds.

ECMWF: WBPT, 1000-500 thickness, MSLP and 6h rain chart for Sat 06Z

River and Surface Water Flood Risk

Soils are mostly waterlogged countrywide, or at least in saturated conditions. Rivers are already elevated in the Northern half of the country, in response to appreciable rainfall over the last week. Over the coming days, multiple separate spells of precipitation will further exacerbate the flood risk across the country. Localised flooding is expected over the weekend and into next week, particularly in the Northern half of the country.

Coastal Flood Risk

We are in a period of Spring (High) Tides. The combination of Spring (High) Tides, strong onshore winds and storm surge associated with the low pressure systems to the south-west of Ireland tonight and into Saturday, is likely to increase the risk of localised coastal flooding, particularly in flood-prone areas along the East Coast (when coincident with High Tides and strong onshore winds).

Becoming wet and windy tonight. Status yellow rainfall warning issued.

The first deep area of low pressure will begin to track to the south of Ireland tonight bringing a band of rain northwards across the country. A status yellow rainfall warning will come into effect from 3am for Wicklow and Wexford with heavy rain bringing accumulations of 30 to 40mm and a risk of localized flooding overnight.

Further to this easterly winds will increase fresh to strong and gusty overnight, while there is a status yellow gale warning in effect from Valentia to Loop Head to Slyne Head. While the winds will generally remain below Status Yellow level overland they will be very strong for the less common and often less sheltered easterly direction.

Becoming cooler on Saturday with sleet and snow on higher ground.

With cold air to the north in close proximity and moving southwards gradually on Saturday morning, precipitation will turn to sleet or snow over higher ground with accumulations possibly building quite quickly. This will lead to hazardous condition, especially through the Wicklow Mountains.

The precipitation will clear southeastwards during the afternoon and the winds will ease.

Saturday night starts off cold and frosty with rain sleet and snow moving in from the west by morning.

While Saturday night will start off cold with some clear spells and an early frost, leading to icy patches, in many northern parts, a further spell of rain, sleet and snow will cross the country early on Sunday.

Greatest risk of snow in northern parts

The northern half of the country looks likely to see the greatest risk of sleet and snow with some accumulations, however warmer temperatures in the south will slowly move northwards with sleet and snow gradually transitioning back to rain in most areas. It will be a cold day however with afternoon highs of just 1 to 4 degrees in most areas, while Munster will remain warmer.

While an advisory has been issued for the weekend, further weather warning are likely and our warnings page should be monitored for updates.

But whatever the weather please follow the public health advice and help keep everybody safe from COVID-19.

A Sudden Stratospheric Warming (SSW) - January 2021

By Climatologist Paul Moore

The stratospheric polar vortex (SPV) is a rotating vortex of cold air high up in the stratosphere over polar regions. It forms every winter in the Northern Hemisphere and the strength of the Northern Hemisphere SPV has a significant influence on the Northern Hemisphere mid-latitude weather patterns. When the SPV is in a strong symmetrical state, it helps to maintain westerly momentum in the troposphere over polar regions and in the mid-latitudes, leading to our typical winter pattern of a strong west to east North Atlantic jetstream, bringing storms and weather fronts over Ireland from the west or southwest and keeping it mild and wet. When the SPV is in a weakened or non symmetrical state, it can lead to the weakened jetstream behaving more like a meandering river with blocking high pressure forming in our region, bringing the possibility of colder, drier weather.

When a weakened SPV goes through further disruption, it can lead to what is know as a Sudden Stratospheric Warming (SSW) event, which refers to the reversal of the zonal winds in the Stratosphere from westerly to easterly, along with a rapid jump in temperatures in the winter polar stratosphere that leads to a complete breakdown of the SPV. A SSW is now defined to have happened when the mean zonal wind (ZW) at 60°N and 10hPa (approx. 30km high) reverses to easterly. A SSW event usually has a significant impact on the tropospheric weather patterns in the mid latitudes. Following a SSW, there can be an equatorward shift of the tropospheric jetstream with associated cold conditions over northern Europe and these impacts can be long lasting. Every SSW is different and less than half of them lead to colder conditions in Ireland. For example, the SSW in February 2018 led to the ‘beast from the east’ and storm Emma, whereas the SSW in January 2019 had no significant impact here, due to the easterly winds not propagating down into the troposphere from the stratosphere. See more about the 2018 SSW event in a report on Storm Emma here.

The current state and forecast for the SPV

The SPV has been below average strength through most of December 2020 (pink line—left panel below) and is forecast to continue weakening (orange line –left panel below) to below zero m/s, which means changing from westerly to easterly. This signifies a technical SSW. The mean zonal winds at the bottom of the stratosphere have also been at very low levels (pink line— right panel below), and are forecast to decrease to record low levels over the next week (orange line– right panel below). This has been, and continues to be a contributing factor in the blocking high pressure systems we have seen in our region lately. The lack of westerly momentum at the bottom of the stratosphere helps to slow down the North Atlantic jetstream in the troposphere and leads to it meandering like a river, north to south, resulting in a more blocked pattern in the mid latitudes. https:// acd –ext.gsfc.nasa.gov/Data_services/met/ann_data.html#ncep_clim_stats_nh

What this reversal looks like can be seen in the below charts. These show the zonal mean wind averaged around the globe at each latitude line. The orange and red colours signify westerly winds and the blue signify easterly winds, with the numbers on each contour showing the m/s value. The values on the x-axis represent latitude, with EQ meaning the Equator. The values on the y-axis represent height in hPa. For example 10 hPa is approximately 30km high and is in the stratosphere, where as 200 hPa is approximately 10km high and is the top of the troposphere. On the 29th December 2020 (left panel below) the zonal winds high up in the stratosphere between 60 and 90N were between 20 and 60 m/s westerly and the sub-tropical jetstream, at 30N and 200hPa height was at 40m/s westerly. The forecast for the 5th January 2021 (right panel below) show the polar stratospheric winds have reversed to between 20 and 40 m/s easterly and are beginning to propagate down into the lower stratosphere. The sub-tropical jetstream averaged around the whole globe has intensified to 50 m/s. https://www.geo.fu –berlin.de/ en/met/ag/strat/produkte/winterdiagnostics/index.html

In the below charts, looking down from a northern hemisphere point of view at the 10 hPa height level (at the same times as above) the temperatures are represented by colours, with the °C values on the left and the geopotential height is represented by contours. On the 29th December 2020 (left panel below), the already weakened polar vortex, with its low pressure centre just to the northwest of Scandinavia, is surrounded by tightly packed height contours representing the strong westerly winds rotating anticlockwise around the vortex. The ZW at that stage was 25.2 m/s and can be seen at the bottom of the chart. There is already a strong warming signal over Siberia represented by the red colours. On the forecast chart for the 5th January 2021 (right panel below) the warming signal and associated high pressure has worked its way around and is penetrating into the polar vortex, pushing it further away from the north pole and almost splitting it. The more this high pressure pushes in over the north pole, the more the ZW changes from westerly to easterly. The ZW has reversed to easterly at this stage, shown by the -3.2 m/s at the bottom of the chart.

It is uncertain how this will affect our weather in the coming weeks as we are already in a very blocked setup. It could kick-start the westerly momentum in our region, at least temporarily, as the SPV is pushed over Scandinavia, leading to a strengthening of the North Atlantic jetstream, resulting in a more typical winter weather pattern for Ireland. It could also prolong and intensify the high latitude blocked setup leading to cold polar air masses flooding south into northern Europe or elsewhere in the mid latitudes.

Monthly Weather Forecast

Met Éireann are now issuing monthly forecasts twice a week, at 5pm every Tuesday and Friday, beginning 5th January. It will be available here in the Forecast menu. Monthly forecasting covers the time range of around 10 to 40 days ahead and is really more correctly described as sub-seasonal or extended-range. It is a time scale in between medium-range weather forecasting (10-day)* and seasonal forecasting (3 monthly).

Storm Bella: December 26th/27th 2020

By Meteorologist, Liz Walsh and Hydro-meteorologist, Stephen Carey

Posted: 1400 24th December, Christmas Eve

Whilst Christmas Day itself promises to be a generally quiet day weather wise with increasing cloud, and patchy rain and drizzle, mainly over northwestern areas, our weather looks set to turn much more unsettled as we head into the festive weekend.

A briefly milder spell of wet and windy, potentially stormy, weather is expected on Saturday in association with Storm Bella named by the British Met Office earlier today, with much colder weather following for Sunday and into early next week.

Storm Naming Form Storm Bella

Some very cold air currently emerging from northwest Canada and Greenland, is expected to meet relatively warm air over the western Atlantic, resulting in a powering up of the Polar Front Jet Stream. A complex low pressure system, named Storm Bella by the UK Met Office this morning, is tracking eastwards over Greenland today (Christmas Eve). The low looks set to engage the developmental zone of this powered up Jet Stream, which will help to deepen it to the north of Iceland on Friday, Christmas Day. Storm Bella will be tracking eastwards over parts of Iceland by Saturday afternoon, and is expected to have grown into quite a large feature by then, generating a vast swathe of gales, westerly veering northerly, across the North Atlantic as it interacts with the Azores high to the south. Storm Bella is then forecast to track southeastwards towards the North Sea whilst deepening a little more into Saturday night bringing a spell of wet and very windy weather over Ireland for Saturday afternoon/evening/night as an associated squally cold front tracks southeastwards over the country.

Animation courtesy of the ECMWF showing Mean Sea Level Pressure (white lines) overlaid with 500hPa Geopotential Height. Geopotential heights are lower in cold airmasses and higher in warm airmasses. So, the darker purple colours, indicative of lower geopotential heights are also indicative of very cold air high up in the Atmosphere, while the green-yellow-orange colours are indicative of relatively warmer air high up in the Atmosphere.

A yellow level wind warning has now been issued for Saturday for Connacht, Donegal and western parts of Munster, valid from Midday on Saturday through to 6am on Sunday, and the situation will continue to be monitored by Met Éireann’s meteorologists through Christmas Day and updated as required.

The UK Met Office have issued yellow and amber wind warnings over parts of England and Wales for Saturday and Sunday.

Coastal Flood Risk

The combination of forecast storm surge and very unsettled, potentially stormy conditions, associated with a Storm Bella on Saturday/ Sunday, is likely to increase the risk of coastal flooding (spray over-topping and localised wave over-topping), especially in flood-prone areas along Irish coasts (particularly when coincident with High Tides and onshore winds).

Please see the approximate High Tide times below for Saturday & Sunday:

Saturday (St Stephen’s Day) 26^th December 2020:

West and South coasts: 02:00 – 04:00 & 14:00 – 16:30 (early morning and afternoon)

East coast: 08:00 – 09:30 & 20:30 – 22:00 (morning and evening)

Sunday 27^th December 2020:

West and South coasts: 02:30 – 04:30 & 15:00 –17:00 (early morning and evening)

East coast: 09:00 – 10:30 & 21:00 – 22:30 (late morning / and late evening)

River Flood Risk

Soils are mostly saturated countrywide, and waterlogged in some places. Rivers are already elevated in the western and southern half of the country in response to appreciable rainfall over the last week or so. Whilst forecast rainfall may not reach rainfall warning criteria, heavy rainfall may cause localised flooding.

Turning colder again from Saturday night onwards

Behind the cold front on Saturday night, some rather cold and deeply unstable air will bring showers on Sunday and early next week. Some of these showers will have a wintry flavour to them, with a mix of rain, hail, sleet and possibly some snow likely. People travelling by road from Saturday night onwards are advised to watch out for the risk of icy stretches and poor visibility in showers.

Stay up to date with Met Éireann’s weather and warnings throughout this Christmas period at:

https://www.met.ie/forecasts/national-forecast

https://www.met.ie/warnings

Wet and windy weather on Tuesday 15th and Wednesday 16th December

by Linda Hughes, meteorologist, and Matthew Roberts, hydrometeorologist

Very unsettled conditions are forecast for Ireland this Tuesday night into Wednesday morning, with heavy rain leading to a risk of flooding and the potential for very strong winds and damaging gusts. For any weather warning updates, please keep in touch with https://www.met.ie/warnings/today.

Synoptic Pattern

A broad scale upper-level area of low pressure, along with an associated surface low, will become established to the west of Ireland on Tuesday. A southerly component of the Polar Jetstream (a fast flowing air current around 10km above the Earth’s surface) will strengthen over Ireland during Tuesday (Fig 1.). This Jetstream can steer surface low pressure systems towards Ireland and intensify them, depending on the location of the low relative to the Jetstream.

Fig. 1: The Jet-Stream across the North Atlantic from 12UTC Tuesday 15th December to 06UTC Wednesday 16th December, showing wind speeds at a height of 300hPa (Forecast chart issued by ECMWF).

Forecast Track of Low Pressure

A secondary low pressure system is forecast to form in the Mid-Atlantic on Monday and track eastwards through Monday night and Tuesday morning, deepening steadily. There is then generally good agreement between forecast models that the system will track towards Ireland, however there are disagreements between the models on its speed, intensity and track. Until these are resolved, there is uncertainty in the exact impacts on Ireland.

Fig. 2: ECMWF forecast for position of low pressure system at 12UTC Tuesday 15th December.

The 00UTC 13th December model run of ECMWF (Fig. 3) is forecasting that the low pressure system will deepen as it approaches the southwest coast of Ireland from the southwest, with a minimum pressure of 968 hPa at 00UTC Wednesday. The depression is then forecast to track close to the west coast of Ireland, weakening.

Fig. 3: ECMWF forecast of wind speed and mean sea level pressure at 00UTC and 06UTC Wednesday 16th December.

Fig. 4 illustrates the uncertainty in the positioning of the depression at 00UTC Wednesday, with the shaded areas showing the uncertainty. The ECMWF ensemble product consists of 51 separate forecasts made by the same computer model, all activated from the same starting time but with slightly different initial conditions. Ensemble forecast products give forecasters a picture of the range of possible outcomes in a weather event.

Fig. 4: Mean sea level pressure forecast and standard deviation (shaded) for 00UTC Wednesday16th December (Forecast from ECMWF).

Rainfall

A band of heavy rain is forecast to move into the southwest on Tuesday evening, extending across the country during Tuesday night. The rain is expected to clear from most areas on Wednesday morning, although the west coast could see further heavy rain through the morning. While the rain will be heavy, its progression should be quite quick. However, due to soils being saturated or waterlogged there will be a risk of flooding (see below for further comments on flood risks). Based on the latest forecast, 6-hour accumulations of 10 to 15mm are expected in parts of the southwest and west. As indicated in Fig.5 (Valentia used as an example) there is uncertainty in the total precipitation expected from later Tuesday into Wednesday.

Fig. 5: ECMWF ensemble forecast of total precipitation at Valentia

Wind

The current deterministic forecast by ECMWF tracks the depression along the west coast of Ireland on Tuesday night. The strongest winds are expected to be on the southeastern side of the system, so very strong south to southeast winds are expected in the south initially and then also in the east overnight Tuesday into Wednesday morning. There is also the potential for severe gusts.

Fig.6: ECMWF wind speed forecast (colours indicate warning levels).

Any changes to the forecast of the track of this depression will impact the locations of the strongest winds.

Coastal Flood Risk

We are in a period of Spring (High) Tides. The combination of Spring (High) Tides and very unsettled, potentially stormy, conditions associated with a depression on Tuesday/Wednesday, is likely to increase the risk of coastal flooding (spray overtopping and localised wave overtopping), especially in flood-prone areas along all Irish coasts (particularly when coincident with High Tides and onshore winds).

Please see below the approximate Spring High Tide times below for Tuesday and Wednesday:

Tuesday 15^th December 2020

West and South coasts: 04:30 – 07:00 & 17:00 – 19:30 (early morning and evening)
East coast: 10:00 – 12:00 & 22:30 – 00:00 (late morning and late evening)

Wednesday 16^th December 2020

West and South coasts: 05:30 – 08:00 & 18:00 – 20:30 (early morning and evening)
East coast: 11:00 – 12:30 & 23:30 – 01:00 (late morning/midday and late evening)

River Flood Risk

Soils are mostly waterlogged countrywide, or at least in saturated conditions. Rivers are already elevated in the western half of the country, in response to appreciable rainfall over the last week or so. Over the coming days, multiple separate spells of rain (whilst individually these may not reach rainfall warning criteria) will further exacerbate the flood risk. Localised flooding is expected in the western half of the country over the next week.

Early December cold snap 2020

A significant change in our weather pattern will occur this week with a cold polar maritime airmass sweeping across the country. A cold front will extend southeastwards across Ireland Tuesday night and this will mark the beginning of a noticeably colder and more wintry spell of weather.

Synoptic Pattern

The change in weather is being caused by the amplification of the polar jetstream over the North Atlantic which is aiding the development of a blocking high pressure system which will extend from the Azores to Greenland. This will enable polar air flood southwards towards Ireland and northwestern Europe. However, as this cold air moves over the relatively warm seas of the North Atlantic, the depth of cold will be modified resulting in a wintry mix with snowfall mainly restricted to high ground, but with some snowfall to lower levels possible at times later this week.

Figure 1: A forecast chart from the ECMWF for Thursday 3 December at 1200UTC illustrating 850hPa wet-bulb temperatures, 1000-500hPa thickness levels and mean sea level pressure. The chart shows high pressure blocking developing in the North Atlantic with cold air being advected southwards from Greenland and Iceland

So what can we expect?

From Wednesday onwards it is going to feel much colder than recently with a strong west and northwest wind developing bringing an added wind-chill factor. Daytime temperatures will be in low single figures and night-time temperatures will be around zero or lower at times.

There’ll be a mix of sunny/clear spells and showers, most of the showers will be of rain and hail but some will turn wintry, particularly during Thursday and Friday and over high ground with some snowfall likely. Frost and ice is expected in many areas by night and this will lead to tricky road conditions with the frost lingering in places late into the morning.

Figure 2: Minimum air temperatures forecast to occur between Thursday night and Friday morning (3-4 December) from the ECMWF deterministic model

Hail is expected to be quite a common sight from mid-week as the atmosphere will be very unstable with very heavy showers forming. A large contrast in temperature between the sea surface and lower atmosphere will enable deep convective showers to develop over the seas around Ireland and these will move onshore bringing hail and thunder. Hail can be very hazardous for road-users and has resulted in multiple road-collisions in recent years.

Aftermath of hail shower at Birdhill in County Tipperary which caused multi car collisions on 11th December 2019. Courtesy of James O’Dwyer via Stephen Smyth

Transport Infrastructure Ireland (TII) operate over 100 automatic road weather stations, located on the side of many of our major roads and motorways. These stations monitor the weather conditions on our roads such as road temperature, air temperature, dew point temperature, wind speed and direction. Met Éireann provide forecast temperature profiles and surface conditions for all of these stations every day through the winter season.

Advisories and Warnings

But whatever the weather please follow the public health advice and help keep everybody safe from COVID-19.

Howling Halloween: Very wet and windy weather on the way

Meteorologist’s Commentary updated 1700, Saturday 31/10/2020

by Liz Walsh, Meteorologist, Forecast Division, Met Éireann.

Storm Aiden is currently situated just off the western Isles of Scotland, now well clear of Ireland’s shores. Its closest approach was earlier this morning when the centre was within 100 to 150 nautical miles of northwestern coasts.

6am Analysis overlaid with satellite.

The associated frontal system tracked eastward over the country this morning. The cold front in particular was quite squally and gusty and some line convection developed on its back edge. Some high accumulations occurred in parts of Connacht and Donegal overnight.

Radar/Satellite composite at 9am, Saturday 31st October 2020

Storm Aiden appears to have tracked slightly further west than what some of the forecast guidance was suggesting yesterday, so the strong winds in the southeast were weaker than the forecasted orange level. However, provisional observations for the more western counties, show we breached orange (and briefly red!) warning levels at a number locations.

A selection (but by no means exhaustive) list of the highest 10-min winds and gusts that occurred (provisional) include:

Further spells of wet and windy weather are expected tonight and again from tomorrow (Sunday) evening.

A yellow wind warning is in effect for the windy conditions Tonight, with potential for further weather warnings for later on Sunday and into Monday.

Stay up to date with the forecast at met.ie

For all our weather warnings go to https://www.met.ie/warnings

Meteorologist’s Commentary updated 1700, Friday 30/10/2020

by Liz Walsh, Meteorologist, Forecast Division, Met Éireann.

Storm Aiden was named by Met Éireann this morning, with orange level winds expected to affect Ireland for a time from early tomorrow morning.

Storm Aiden is expected to rapidly deepen in the development zone of the Jet Stream between midday today (Friday 30th Oct) and midday tomorrow (Saturday, 31st Oct) as it tracks towards and over western parts of Ireland. The storm is expected to be positioned to the northwest of Ireland by midday on Saturday.

Above animation shows the Jet Stream visualized here in purple with surface pressure marked in black. Courtesy of the ECMWF.

Current warnings:

A yellow level wind warning is in effect from 0200 (2am) to 1600 (4pm) on Saturday 31^st October 2020 countrywide

The UK Met Office has also issued a yellow wind warning for Northern Ireland valid from 6am to 9pm which incorporates western parts of Britain also

Two Orange level wind warnings are also in effect valid for a shorter time period on Saturday:

From 0500(5am) to 1000(10am) winds will reach orange level at times in Kerry, Cork, Waterford, Wexford, Wicklow, Carlow & Kilkenny
From 0800 (8am) to 1600 (4pm) winds will reach orange level at times for Clare, Galway, Mayo, Sligo and Donegal

As mentioned below during previous updates to this commentary, further spells of wet and windy weather will occur through the rest of the weekend and into Monday morning.

More wet and windy weather will arrive Saturday evening/night in association with the remnants of ex-hurricane zeta with rain spreading from the southwest and gales developing in coastal areas overnight.

As we head through Sunday further wet weather looks set to move in from the Atlantic. A spell of strong winds is also possible for southern counties on Sunday night, but there is still some uncertainty as to how this will play out.

Above picture shows ECMWF’s forecast Temperature profile at 850hPa (approximately 1.5km above the earth’s surface) overlaid with Surface Pressure in Black for Midnight tonight.

Further rain and wind warnings are possible through the weekend, so stay up to date with the forecast.

For all our weather warnings go to https://www.met.ie/warnings

Meteorologist’s Commentary updated 1500, Thursday 29/10/2020

by Gavin Gallagher, Meteorologist, Forecast Division, Met Éireann.

Wet and very windy weather over the Halloween weekend as a series of vigorous Atlantic weather systems pass close to Ireland.

After a settled day on Friday we will have a very unsettled spell of weather from Friday night through to Monday evening, with 3 separate low pressure systems tracking close to Ireland, bringing wet, windy and possibly stormy weather. Each system is around 24 hours apart, with the first impacting Ireland Friday night into Saturday, the next Saturday night into Sunday, with the third later Sunday into Monday.

So this is not just one event, but rather a series of low pressure systems affecting us over a three-day period, with cumulative impacts from rainfall, strong winds and high seas. The series of low pressure systems can be seen on the Wind Streamlines animations below.

The above animations show the forecast airflow over the north Atlantic and Europe. (First: Friday 9pm to Sunday 9am. Second: Sunday 6am to Monday 9am)

The colours use the warning levels of yellow, orange and red for wind speeds with purple indicating hurricane force winds.
The airflow is indicated by streamlines (Think of a streamline as the path a child’s helium balloon will make if accidentally released to drift with the wind. Each streamline represents the trajectory of the air at that location).

One of the depressions that will impact us will be the remnants of ex-hurricane Zeta, which is currently (Thursday 3pm) over the eastern United States.

Tropical Storm/ex-Hurricane Zeta currently over the eastern United States will move out into the North Atlantic tonight. Above is a forecast track of Zeta issued from the National Hurricane Centre (NHC))

Hazards this weekend:

Spells of heavy rain will lead to surface and river flooding. All soils are saturated across the country at present, so additional rainfall will quickly run-off into rivers. The heaviest and most persistent of the rain is likely in the south and west of the country.

Very windy/stormy at times with some severe and damaging gusts possible. The strongest of the winds are likely in southern, western and northwestern areas, particularly near coasts.

Some coastal flooding possible also as we have very high seas at the moment, combining with surge, high tides and onshore winds over the weekend. Areas most at risk, again in the south, west and northwest.

Met Éireann’s high resolution HARMONIE model, showing the position of the first low pressure system at 9am on Saturday, with 3 hour rainfall totals.

Current Advisories/Warnings:

An Advisory is in place from Friday night through to Monday evening, for all areas.

A status yellow wind warning is in place for all areas for Friday night and Saturday. This warning will be refined and possibly upgraded tomorrow, Friday. With further warnings to be issued for wind and rain over the weekend.

Please consult your local warnings from Met Éireann on a day by day basis https://www.met.ie/warnings/today

The above animation shows mean sea level pressure and precipitation from 6am Friday to 6pm Monday.

The heaviest of the rainfall from these depressions will be during night-time hours, Friday night into Saturday, Saturday night into Sunday and Sunday night into Monday, so there will be drier intervals by day. It will be relatively mild also as these systems drag tropical air up over Ireland, with temperatures 2 or 3 degrees above normal for this time of year. Highs of 15 degrees on Saturday, up to 16 degrees on Sunday and Monday.

Our weather will settle down from midweek next week, becoming mostly dry and cool, with light winds as high pressure takes charge.

Meteorologist’s Commentary issued 1500, Tuesday 27/10/2020

Howling Halloween by Matthew Martin, Meteorologist, Forecast Division, Met Éireann.

Weather conditions will be very unsettled across Ireland this week with the disturbed weather pattern expected to persist for the Halloween weekend. Please keep updated with our weather warnings at https://www.met.ie/warnings/today

Synoptic Pattern

At this time of year, the thermal gradient across the North Atlantic is steepening with the clash between very cold air near Greenland and warm air feeding northwards from the tropical Atlantic creating a very strong Polar Jet-Stream aloft. As the Polar Jet-Stream strengthens (a fast flowing air current around 10km above the earth’s surface) it can act to enhance the ferocity of our typical low pressure systems in the North Atlantic.

(Fig 1: The Jet-Stream across the North Atlantic is expected to intensify this week with speeds in excess of 165 knots forecast at a height of 300hPa by 00UTC Saturday October 31st. Forecast chart issued by ECMWF)

In addition, as the record breaking Atlantic hurricane season continues, following quickly in the wake of ex-Hurricane Epsilon which tracked towards Iceland yesterday, it looks like more moisture will be added into the frontal systems in the Atlantic later this week as ex-Hurricane Zeta tracks out of North America on Friday.

(Fig 2: Tropical Storm/ Hurricane Zeta is forecast to track over North America this week before exiting into the North Atlantic on Friday. Above is a forecast track of Tropical Storm/Hurricane Zeta issued from the National Hurricane Centre (NHC))

The combination of these factors and the position of the Polar Jet-Stream looks set to bring a period of very wet and potentially very windy weather across Ireland this week.

Rainfall

One of the main concerns in the Forecasting Office this week is the amount of rainfall expected over the next several days. Successive frontal systems are expected to move across Ireland during the week bringing periods of heavy rain. The heaviest and most persistent rain is expected to affect Munster, Connacht and west Ulster but all areas will see spells of heavy rain this week. Weather Warnings have already been issued for Thursday and further warnings can be expected for this weekend. https://www.met.ie/warnings/today

(Fig 3: Accumulated Rainfall forecast from the ECMWF Ensemble System illustrating the mean, maximum and minimum forecast total rainfall from Tuesday 00UTC 27th October to Saturday 00UTC 31st October)

Flooding

River Flooding

Currently river levels are elevated in the Western half of the country, particularly in Connacht, Donegal and parts of Munster. River levels are expected to increase further in response to warning-level rainfall on Thursday, leading to some river flooding. Therefore, any additional rainfall from Friday onwards will further compound the flooding issues in these areas.

Coastal Flooding

We are due to enter a period of Spring (High) Tides on Saturday. The combination of high seas and strong winds or stormy conditions associated with any low pressure systems may increase the possibility of coastal flooding, especially in flood-prone areas along the Atlantic coast on Saturday (particularly when coincident with high tides).

(Fig 4: Total Sea and Swell Height & Direction forecast for 12UTC Saturday 31st October from ECMWF deterministic model, illustrating the high seas and swell forecast off the west coast of Ireland on Saturday)

Wind

Numerous low pressure systems are expected to track close to Ireland this week bringing gales to our sea areas and strong winds on land. At present, there remains large uncertainty on the timing and magnitude of any single wind-event but all areas will experience windy weather this week. As we approach the weekend there is a heightened risk of very windy or potentially stormy conditions developing as low pressure systems in the Atlantic undergo rapid-cyclogenesis (rapid intensification) as they approach our coast. Current numerical weather models (NWP) show the strongest winds associated with these systems staying offshore but this may change in subsequent output.

Fig 5: ECMWF Forecast chart for 06UTC Saturday 31st October showing mean sea-level pressure and 3 hour accumulated rainfall from 03-06UTC)

A note on Storm Naming by Evelyn Cusack, Head Forecast Division.

Met Éireann and the UK Met Office formed a storm naming partnership in 2015 and were joined in 2019 by the Dutch Meteorological Service, KNMI.

There is also a southwest partnership between Meteo France, IPMA (Portugal), AEMET (Spain) and RMI (Belgium) and there have been two named storms so far this season, Alex (1st October) and Barbara (19th October).

Once a storm is named by any National Met Service globally, that name is retained if the storm moves into our waters. For example: Ophelia and Lorenzo were named by the National Hurricane Center (NHC, USA) and Emma by IPMA (Portugal).

This naming of storms by National Meteorological Services has been shown to raise awareness of severe weather and help with citizen safety. A storm is named by a National Met Service when Orange or Red level winds are forecast to impact over a wide land area. Orange or Red level gusts can occur in exposed areas without the event being named. In addition there may be high impact precipitation (rain/snow) associated with the storm system.

Mariners’ records from the 16^th Century show Caribbean Tropical Storms being named after Saints but reliable record keeping of tropical cyclone data within the Atlantic Ocean did not begin until 1851. In the 1950’s the National Hurricane Center (NHC) started naming Tropical Storms in the Atlantic giving them exclusively female names and then in the 1970’s alternating male and female names.

The six lists below are used in rotation and re-cycled every six years, i.e., the 2019 list will be used again in 2025. Names beginning with Q, U, X, Y and Z are not used and if there are not enough names then the NHC moves on to the Greek alphabet: Alpha/Beta/Gamma/Delta/Epsilon/Zeta/Eta/Theta/Iota/Kappa/Lambda/Mu/Nu/Xi/Omicron/Pi/Rho/Sigma/Tau/

Upsilon/Phi/Chi/Psi/Omega.

2020 is only the second year since this naming system began in the 50’s that the Greek alphabet has been used, the first was in 2005.

The only time that there is a change in this list is if a storm is so deadly or costly that the future use of its name on a different storm would be inappropriate for reasons of sensitivity. If that occurs, then at an annual meeting by the WMO committee (called primarily to discuss many other issues) the offending name is stricken from the list and another name is selected to replace it. Several names have been retired since the lists were created. Here is more information the history of naming tropical cyclones and retired names.

The Atlantic hurricane season runs from June 1 through to November 30 each year and the height of the season is in early to mid-September. Tropical systems that form outside of these months are referred to as “off season”, and account for roughly 3% of all storms that form in a given year.

For the latest forecasts go to:

https://www.met.ie/warnings/today

https://www.nhc.noaa.gov/

All known North Atlantic tropical cyclones (since 1851) and Eastern North Pacific tropical cyclones (since 1949)

Generally Unsettled & Potentially Stormy Weather Incoming 24th -28th October 2020

By Meteorologist, Liz Walsh 3.30pm 24th Oct 2020

Latest satellite image from the Goes-East satellite image from 1.30pm today, Saturday 24th Oct 2020. Red Circle is Hurricane Epsilon. Purple Circle on the right is the rapidly deepened low pressure system which gave us those forecasted wet and windy conditions last night. And Ireland in the green circle.

The low centre to the northwest of Ireland is expected to remain slow-moving over the next day or so steering in heavy blustery showers at times and strong and gusty winds, before it tracks east-southeastwards over northern Britain on Monday.

Meanwhile, Epsilon is expected to transition to a mid-latitude low over the western north Atlantic by Monday. Its remnants will then become absorbed into another low pressure system currently tracking eastwards over Newfoundland. Frontal rain associated with this low pressure system containing the remnants of Epsilon, is expected to cross the country on Tuesday. Current guidance keeps the low pressure system itself – and by default the strongest winds – out to the west of Ireland in the central North Atlantic. But as always, Met Éireann’s Meteorologists will continue to monitor the situation for any changes.

The Jet Stream is likely to remain strong through the subsequent outlook period, producing spells of wet and windy weather.

By Meteorologist, Liz Walsh 4pm 22nd Oct 2020

Hurricane Epsilon rapidly intensified to a category 3 Hurricane last night (Irish Time) over the central Atlantic, southeast of Bermuda. It has since dropped in intensity and is currently analysed as a strong category 1 hurricane by the National Hurricane Center. Tropical storm conditions are still expected on Bermuda today. A gradual decrease in intensity is expected as the system starts to move over colder waters and encounters strong winds aloft. Epsilon is still forecasted to curve north-eastwards to the east of Bermuda over the coming days. It is still unclear how exactly Epsilon will impact weather conditions in Ireland but the timeline remains the same – early next week around Tuesday/Wednesday. Met Éireann meteorologists will continue to monitor the system closely as it goes through extra-tropical transition over the next number of days.

Satellite Picture courtesy of NASA from the polar-orbiting satellite Suomi from Yesterday Evening 21^st Oct 2020, with Hurricane Epsilon in its rapidly intensifying phase. (Red Circle). Cloud field associated with what will become Friday night’s low system (Purple Circle) and Ireland in the Green circle.

As referred to below (yesterday’s commentary) though, another Atlantic low pressure system is still expected to engage with the Jet Stream and rapidly deepen during tomorrow Friday (see satellite picture above). The low itself is expected to track between Iceland and Ireland but the associated active frontal system is still expected to cross the country on Friday night and Saturday morning resulting in a period of very strong winds and heavy rain.

Status Yellow Wind and Rain warnings have now been issued for this system.

A status yellow rain warning has been issued for Galway and Mayo valid from 9pm Friday 23^rd Oct to 9am on Saturday 24^th Oct.

2 yellow wind warnings have been issued with different validity times:

A status yellow wind warning has been issued for Donegal, Galway, Mayo, Clare and Kerry valid from 10pm Friday 23^rd Oct to 7am Saturday 24^th Oct.

A status yellow wind warning has also been issued for Cork, Waterford and Wexford valid from midnight to 11am on Saturday 24^th Oct.

These warnings will be reviewed over the next 24 hours and any updates will be issued as required.

For all the latest information go to: www.met.ie/warnings

By Meteorologist, Liz Walsh 2pm 21st Oct 2020

After a period of quieter more slowly evolving weather earlier this month, our weather pattern is looking decidedly more generally changeable and at times very unsettled through the rest of October. As is often the case, this is largely in response to a strengthening of the Polar Front Jet Stream. The Jet Stream is identified as a zone of fast moving air high up in the atmosphere and it is responsible for driving and developing low pressure systems across the Atlantic towards our shores.

The strengthening of the Jet Stream is not unusual at this time of year as the temperature gradient between the tropics and the poles increases in response to the shorter daylight hours as we head into the winter months. The greater the difference in temperature, the stronger the Jet Stream becomes. This goes some way in explaining why we get most of our storms during the winter half of the year as opposed to the summer, although as we have seen recently with Storm Ellen and Francis, storms can and do happen at any time of the year!

How and where low pressure systems interact with the Jet Stream often determines whether a low pressure system will deepen or fill which then determines how impactful the wind and rain associated with that low pressure system will be.

Animation of forecast Jet Stream (Purple) overlaid with Surface pressure (black isobars) from the ECMWF over the next several days.

Over the coming week, the Jet Stream is expected to help deepen areas of low pressure and direct them generally between Ireland and Iceland. Associated Atlantic frontal systems will cross the country resulting in successive spells of wet and windy, potentially stormy, weather, especially this weekend and on into early next week.

On Friday, an Atlantic low pressure system is expected to engage with the Jet Stream and rapidly deepen. The low itself is expected to track between Iceland and Ireland but the associated active frontal system will cross the country on Friday night and Saturday morning resulting in a period of very strong winds and heavy rain.

The next Atlantic low pressure system that will affect Ireland after Saturday, will be early next week and that low pressure system will likely contain the remnants of Epsilon, currently a category 1 Hurricane which is expected to curve northeastwards to the east of Bermuda this weekend. As mentioned in one of our meteorologist commentaries from last month, (see “The 2020 Hurricane Season so far” meteorologist commentary) we passed the peak of Atlantic Hurricane Season quite a while ago. In that commentary, it was also mentioned that: “The delayed warming of the Atlantic Ocean forces the location of extra-tropical transitioning storms northward late in the season so here in Ireland, we are more likely to see the remnants of these storms influencing our weather over the coming weeks and months.” And looking at the current set-up in the Atlantic right now, we can see that situation appears to be developing.

Current NHC forecast for Hurricane Epsilon. Note times are in Atlantic Standard Time 5 hours behind Irish Summer Time.

How Epsilon will interact with the Jet Stream is still uncertain at this stage, but certainly the current guidance across multiple models is suggesting a very deep low will be positioned to the northwest of Ireland in the north Atlantic early next week. This is likely to again bring a period of strong winds and heavy rain to our shores. How strong the winds will be will be dependent on the depth, location and track of the ex-Epsilon low. Whatever the case, Epsilon will no longer be a hurricane at that stage as it will have transitioned to mid-latitude low.

What happens to a hurricane structurally when it transitions?

When a hurricane or tropical system moves up into the higher latitudes, the strong upper level winds (jet stream) cause the storm to speed up.
At the same time, the increase in the wind speed in the upper air almost literally chops off the upper part of the hurricane and sweeps it away
The hurricane is also starting to move over cooler water so its fuel source is depleting from below.
Basically the hurricane structure gets destroyed from above and below.
While the maximum wind often decreases, the wind field spreads out, so the overall impact of high winds actually increases due to the expansion of the wind field. So even though the winds may not be quite as strong as they were when the system was a hurricane, there is a wider area of potential for damage due to high winds owing to the expanded wind field.

Storm Alex named by Meteo France

By meteorologist Gavin Gallagher.

Storm Alex has been named by the French National Met Service, Meteo France.

https://vigilance.meteofrance.fr/fr

The storm is a fast moving area of low pressure that will develop in the Atlantic through Thursday, 1^st October and hit western France Thursday night.

This system will deepen very rapidly, going from 1003 hPa at 11am on Thursday to 971 hPa at 1am on Friday – that’s a deepening of 32 hPa in 14 hours.

At present (5pm Wednesday) what will ultimately become Storm Alex is just a fairly innocuous surface trough out in the Atlantic – currently visible as a band of cloud. However tonight and early Thursday this will interact with a very strong jet stream in the upper troposphere which will rapidly deepen the surface trough into a very powerful cyclone.

Storm Alex will travel eastwards and strengthen through Thursday, entering the Bay of Biscay around 6pm, with winds impacting the west coast of France late Thursday evening, with the system crossing the French coast around midnight. This will bring very strong winds to northwest France on Thursday night with violent storm force 11 winds at sea. Northern Spain will also experience strong winds on Thursday night, with strong winds impacting coastal parts of southern England from Friday morning.

Above is the forecast mean wind speed (in warning colours) from Thursday 12z to Friday 18z from Met Éireann’s High Resolution HARMONIE Model.

This storm will also bring heavy rainfall to northern Spain and much of France, with southern England receiving heavy rainfall early on Friday.

The UK Met Office has issued Yellow Level wind and rain warnings for southern England for Thursday night and Friday

https://www.metoffice.gov.uk/weather/warnings-and-advice

Storm Alex is part of a plunge of colder air pushing down over northwest Europe for the days ahead, with much of the associated precipitation over the Pyrenees and the Alps falling as snow.

Ireland will also feel the effects of Storm Alex with the broader area of low pressure associated with this weather event likely to bring heavy rain across the country later Saturday and early Sunday with a possibility of some flooding. Northerly winds will also strengthen over Ireland Saturday night and Sunday.

Keep up to date with the latest weather warnings at

https://www.met.ie/warnings

The 2020 Hurricane Season so far

By Meteorologist, Liz Walsh

The 2020 Hurricane Season is shaping up to be one of the most active hurricane seasons on record with 20 named storms so far as of Friday 18^th September 2020 at 9am Irish Time.

The average number of storms over the entire season which stretches from June 1 through to November 30 is 12, with 6 of those storms strengthening to hurricane, and 3 of the 12 strengthening to Major Hurricane Strength (classified as Category 3 or more on the Saffir- Simpson Hurricane Wind Scale [1]). Note that a tropical storm is a tropical cyclone that has maximum sustained surface winds ranging from 39-73 mph / 63-119 km/h / 34-63 knots). A hurricane is a tropical cyclone that has maximum sustained surface winds of 74 mph / 119 km/h/ 64 knots or greater.

On the 14^th September, the US National Hurricane Center issued advisories on five tropical cyclones over the Atlantic basin – tying with the record for the most number of tropical cyclones in that basin at one time, last set in September 1971.

Image above from National Hurricane Center on September 14^th 2020.

As predicted by the US National Oceanic and Atmospheric Administration [2], the 2020 season has seen an exceptionally high number of named storms, reaching the letter V (Vicky) as of Monday 14 September. Vicky is the earliest 20^thAtlantic named storm on record. The old record was set by Vince on October 9, 2005. The season lasts until 30 November.

Only the name Wilfred remains, and there are currently two tropical disturbances that are candidates to claim that name over the next day or so. One disturbance located over the south-western Gulf of Mexico currently labelled as Tropical Depression Twenty-two, and another disturbance located a few hundred miles southwest of the Cabo Verde Islands off the coast of West Africa. So it is quite possible that both Wilfred and Alpha could be named by the National Hurricane Center by the end of this weekend.

The hurricane name lists include only 21 letters out of 26, because it is not easy to find 6 appropriate names (for the 6 rotating lists) starting with Q, U, X, Y and Z. In the interests of safety, names must be easily recognizable. In addition, they have to reflect a balance between French, Spanish and English names due to the geographical coverage of the storms throughout the Atlantic and Caribbean, and respect societal sensitivities.

The use of the Greek alphabet (Alpha, Beta, Gamma, Delta, Epsilon, Zeta, Eta, Theta, etc.) has only happened once before in 2005, when six names from the Greek Alphabet were used.

Image above from the World Meteorological Organisation

2005 was a record-breaking year with devastating hurricanes including Katrina, Rita and Wilma, whose names were all retired.

While 2020 is comparable to 2005 with regard to the number of storms, the strength or intensity of the storms so far this year has been less. By the 18^th September in 2005, there had been 4 storms that had become major Hurricanes (classified as Category 3 or more) in the Atlantic Basin (including Katrina) and advisories had begun on what would become the 5^th one, Rita.

In comparison, this year, 2020, there have been only 2 storms that have reached major hurricane status in the basin so far, Hurricane Laura, which reached Category 4 on the 26^th August and Hurricane Teddy which intensified to a Category 4 hurricane last night (Irish time) and is expected to approach Bermuda this weekend. There are still over two months left in the season so there is still time for additional storms to join Laura and Teddy on the list of Major Hurricanes for 2020.

Factors that have been cited by the National Oceanic and Atmospheric Administration to cause this “extremely active” hurricane season include

warmer-than-average sea surface temperatures in the tropical Atlantic Ocean and Caribbean Sea
reduced vertical wind shear (i.e. change in wind speed or direction with change in height)
weaker tropical Atlantic trade winds (Trade winds are the prevailing easterly winds that flow in the Earth’s equatorial region)
an enhanced West African Monsoon (Characterised by changes in surface wind field over Western Africa leading to summer rainfall (wet season) and winter drought (dry season)).

Climate Drivers

A main climate factor driving the above mentioned conditions is the ongoing warm phase of the Atlantic Multi-Decadal Oscillation, which reappeared in 1995 and has been favouring more active hurricane seasons since that time.

Another contributing climate factor this year is the possibility of La Niña developing in the months ahead. La Niña conditions are classified as cooler-than-average sea surface temperatures in the equatorial regions of the eastern Pacific Ocean. Downstream effects of La Niña can further weaken the wind shear over the Atlantic Basin, allowing storms to develop and intensify. Current key indicators are currently at or approaching La Niña thresholds [3].

Image above from NOAA Climate.gov

Hurricane Season and Climate Change

The general consensus among the scientific community at the moment is that the warmer waters we are likely to experience in a warmer world will lead to stronger storms. What is less agreed upon, though, is the number of storms. The general hypothesis is that we expect to see either a decrease in the overall frequency of hurricanes or for it to remain unchanged. This scenario is generally believed to be a by-product of increasing wind shear in the tropics. There is not a perfect consensus on this, however, with a smaller number of studies that simulate an increase in the number of storms. So in terms of number of storms, this is still an area of active research.

An increase in the frequency of very intense storms, however, is generally accepted as a consequence of climate change regardless of whether the number of storms increase/decrease or stay the same. The impacts of this trend are likely to be exacerbated by sea level rise and a growing population along coastlines. There is also the possibility that where cyclones reach maximum intensity will extend further northwards or poleward due to warmer sea surface temperatures.

What can we expect over the next couple of weeks and months?

The large scale pattern looks to generally remain conducive for Atlantic hurricane formation and intensification, although not as conducive as during the past two weeks according to the latest forecasts from Colorado State University of Atlantic Hurricane Activity as of the 16^th September 2020. [4].

We have passed the peak of Atlantic Hurricane Season but there is still a way to go and as we head through the latter part of September and October. The delayed warming of the Atlantic Ocean forces the location of extra-tropical transitioning storms northward late in the season so here in Ireland, we are more likely to see the remnants of these storms influencing our weather over the coming weeks and months.

Image from the National Hurricane Center showing the average spread of storms during the season, with the peak of season on September 10^th.

Met Éireann Podcast

For further information on Hurricanes, have a listen to our Met Éireann Podcast on Hurricanes with National Hurricane Center Senior Hurricane Specialist, John Cangialosi.

https://www.met.ie/education/podcast

For the latest satellite imagery, visit:

https://www.star.nesdis.noaa.gov/GOES/sector_band.php?sat=G16&sector=taw&band=13&length=24

https://www.met.ie/latest-reports/satellites/world-infrared

For the latest weather outlook for Ireland, go to:

https://www.met.ie/forecasts/national-forecast

Works Cited in this commentary:

[1]	National Hurricane Center, “Saffir-Simpson Hurricane Wind Scale,” [Online]. Available: https://www.nhc.noaa.gov/aboutsshws.php.
[2]	NOAA, “Extremely active’ hurricane season possible for Atlantic Basin,” [Online]. Available: 2. https://www.noaa.gov/media-release/extremely-active-hurricane-season-possible-for-atlantic-basin.
[3]	BOM, “Climate Driver Update,” 15 September 2020. [Online]. Available: http://www.bom.gov.au/climate/enso/#tabs=Overview.
[4]	P. J. Klotzbach, M. M. Bell and J. Jones, “COLORADO STATE UNIVERSITY FORECAST OF ATLANTIC HURRICANE ACTIVITY FROM SEPTEMBER 16 – SEPTEMBER 29, 2020,” COLORADO STATE UNIVERSITY, 2020.

Storm Francis - Mon 24th/Tues 25th August 2020

A second named storm in August

Meteorologist Commentary by Joan Blackburn (Deputy Head of Forecasting) and Sinéad Duffy, Met Éireann, Monday 24th August 2020

Storm Francis was named by the UK Met Office due to expected impacts in the UK as a result of the second unseasonable storm in August 2020.

Storm Francis is expected to cross Ireland during Tuesday morning 25 August 2020.

Over Ireland the main concern is for intense rainfall over short periods of time. Orange level rainfall warnings are in operation for Connacht, Donegal, Cavan and Monaghan and also for Southern Coastal Counties of Kerry, Cork, Waterford, Wexford with status yellow rainfall elsewhere. Some flash flooding is likely in places and also this rainfall will further elevate river levels and may result in river flooding as well. The intense rainfall is likely to ease off in southern counties by early Tuesday morning.

It will be very windy, possibly stormy, for a time Tuesday mainly in parts of the south and southeast with yellow wind warnings in operation for Munster and for counties Wexford, Wicklow and Dublin with potential for some damaging gusts.

Caution is advised. With trees in full leaf and many on holidays across the country, impacts could be significant with the potential for damaging winds, heavy rain, and flooding in affected areas.

Tourists in exposed locations in particular will be at risk.

Please sign up for warnings notifications on the Met Éireann app and get the latest warnings https://www.met.ie/warnings and www.metoffice.gov.uk

Figure 1. Rain and Wind warnings associated with Storm Francis (as at 7pm 24rd August 2020)

Figure 1. Rain and Wind warnings associated with Storm Francis (as at 7pm 24th August 2020)

Storm Francis is forming in the Atlantic to the southwest of Ireland as a low pressure deepens rapidly. The extensive bands of cloud and rain are approaching quickly.

Figure 2. EUMETSAT animation of Storm Francis on 24th August 2020

The warnings may be updated as the forecast models are updated, so please keep up to date on the website and apps.

https://www.met.ie/warnings

https://www.met.ie/forecasts/national-forecast

https://www.met.ie/forecasts/marine-inland-lakes/sea-area-forecast

Figure 3. Met Éireann’s high-resolution Ensemble Prediction System (IREPS) showing the range of possibilities of 24 hour rainfall amounts.

Climate perspective

As our planet warms, so does our atmosphere. Warmer air has the ability to hold more moisture. Here in Ireland we have seen an increase in average annual rainfall by about 6% over the last 30 years as compared to the previous 30 years. The latest climate model projections suggest Ireland will likely see more frequent heavy rainfall events, as our planet continues to warm.

Named Storms

Storm Francis is the sixth named storm from the 2019/2020 storm list of the Met Éireann, UKMO and KNMI partnership. It is the ninth named storm overall.

The first one, storm Lorenzo, was named by the National Hurricane Center in the USA. Lorenzo originated as Hurricane Lorenzo, the eastern- and northern-most category 5 hurricane ever recorded in the Atlantic Ocean but it weakened considerably as it stalled off the northwest coast and produced few impacts as it tracked over Ireland on Friday 4th October 2019.

Storm Elsa (18th December 2019) and Storm Jorge (29th February 2020) were named by the IPMA, the national meteorological service of Portugal, and AEMET, the national meteorological service of Spain, due to their forecasted impacts in the Iberian region.

Figure 4: Storm names for 2019/2020 season

Storm Ellen

Storm Ellen brings unseasonably wet and stormy August weather

Meteorologist’s Commentary by Evelyn Cusack, Head of forecasting, Met Éireann Tuesday, 18^th August 2020

Met Éireann has named Storm Ellen for disruptive and potentially damaging winds Wednesday evening (19th) and throughout Thursday (20^th). Due to the combination of storm surge, spring tides and onshore winds there is a risk of some coastal flooding. There is a risk also of some inland and river flooding with some potentially heavy, thundery downpours.

Status Orange/Yellow wind warnings are in effect for the Island of Ireland and will be updated Wednesday morning. Orange level impacts may potentially occur over any part of the Island and tourists in exposed locations in particular will be at risk for these unseasonable stormy and wet conditions. Please sign up for warnings notifications on the Met Éireann app and get the latest warnings https://www.met.ie/warnings and www.metoffice.gov.uk

Fiure 1: Warnings for Ireland issued Tuesday 18/08/2020 for Wednesday/Thursday

Figure 1: Warnings for Ireland issued Tuesday 18/08/2020 for Wednesday/Thursday

Storm Ellen is forming over the Atlantic fuelled by the remnants of Tropical Storm Kyle as shown here in Figure 2 which is a display of Airmass temperature and satellite imagery from the European satellite, Meteosat.

Figure 2: A large circulation in mid-Atlantic fuelled by the interaction of the remnants of tropical storm Kyle and the jet-stream.

Ellen is forecast to move over the southwest of Ireland Wednesday evening, tracking northwards over the country during Wednesday night and daytime Thursday. Gusts generally of 80 to 100km/h can be expected and potentially gusts may exceed 130km/h in some exposed coastal and mountain locations and some lower locations due to funnelling effects.

https://www.met.ie/forecasts/atlantic-charts/precipitation-pressure

Figure 3: Storm Ellen is forecast to track in over Ireland from the Atlantic

There is still a high degree of uncertainty in the exact track of the storm and there is a considerable spread in possibilities over Ireland with some models indicating that the east may get the strongest winds. The warnings will be updated Wednesday morning but here is the 18Z run of the Met Éireann high-resolution model, HARMONIE. It is an ensemble prediction system (IREPS) with 11 different possible tracks and outcomes. Orange level impacts may potentially occur over any part of the Island.

Figure 4: Met Éireann’s high-resolution Ensemble Prediction System (IREPS) showing the range of possibilities of the severe winds.

With trees in full leaf and peak numbers on holidays in Ireland, impacts could be significant with damaging winds, heavy rain, and large waves along the coast. Strong winds overland, high, potentially dangerous, waves can occur on lakes as well as along coasts and over high ground.

Storm Ellen is the fifth named storm from the Met Éireann, UKMO and KNMI storm list of 2019/2020. It is the sixth named storm overall as the first one, storm Lorenzo, was named by the National hurricane Center. Lorenzo originated as Hurricane Lorenzo, the eastern most and northern most category 5 hurricane ever recorded in the Atlantic Ocean but weakenend considerably as it stalled off the northwest coast and produced few impacts as it tracked over Ireland on Friday October4^th2019.

Figure 5: Storm names for 2019/2020 season

Figure 6 is the Storm naming form Met Éireann shared with its partners the UK Met Office and KNMI, the Dutch Meteorological Service in the West group and the Southwest group consisting of Portugal, Spain, France and Belgium when we named Storm Ellen.

Figure 6: Storm Naming Form for Storm Ellen

Updates will be issued Wednesday morning. Extreme caution is advised.

https://www.met.ie/forecasts/marine-inland-lakes/sea-area-forecast

https://www.met.ie/warnings

https://www.met.ie/forecasts/national-forecast

A Typical Late-Summer Type Setup

Published Friday 14th of August

During the last week, Ireland, and to a much more exceptional extent our neighbours in southern Britain, have been experiencing very warm and humid conditions. This has been due to very warm or hot air over the European continent being transported northwards over our part of the world.

But that hot continental air has had low pressure associated with it. The combination of low pressure and warm humid air produced conditions that triggered thunderstorm activity. Torrential downpours and frequent thunder lightning occurred over southern parts of country on Wednesday night.

Another aspect of the conditions over the last week has been the generally light winds associated with what meteorologists would describe as a slack pressure pattern. The low pressure that has been affecting us hasn’t been particularly low – varying between 1010 and 1014 hPa – and rather than a tightly coiled feature that we would tend to witness with a storm system, the pressure pattern over us looks kind-of bland with big spaces between the isobars and accordingly, generally light winds.

06z Analysis on Thursday 13 August 2020

Where Thunderstorms have formed, they have been quite slow-moving – because of the light winds -and they have therefore managed to dump some high rainfall amounts leading to significant spot flooding.

There will be little change in the pressure pattern out to around Tuesday next week so the risk of heavy or potentially thundery downpours will remain until then, with the exact detail varying day to day and dependent on parameters like cloud cover and daytime heating.

Later Next Week:

Looking ahead to around midweek next week, we have to look further afield. And our meteorologists are keeping an eye on developments in the Atlantic. Currently we’re following a low pressure area which is expected to form southwest of Greenland (A in the picture below) and how that is going to interact with another feature which is currently off the coast of North Carolina (B in the picture below).

ECMWF Surface Pressure Chart over-layed with 850hPa temperatures for Saturday 15 August

The “B” system has attracted the interest of National Hurricane Center forecasters who are monitoring it for tropical development:

Regardless of what ends up happening, the interaction of the cold air coming down from Greenland and the relatively warmer air coming off the east coast of the US, is likely to result in a powering up of the Jet Stream across the Atlantic. With a strengthening of the Jet Stream, the return of an Atlantic-influenced westerly or south-westerly regime seems likely by around midweek next week, with Atlantic low pressure likely to bring spells of rain and noticeably windier conditions than of late.

The Year So Far

The Year So Far

Written by Paul Moore and Valerie Watters.

A very strong Stratospheric Polar Vortex leading into February helped to ignite the North Atlantic Jet stream, which brought numerous deep depressions towards North-western Europe. This led to a very wet and very windy month in Ireland, with temperatures a little above average overall.

As the Stratospheric Polar Vortex began to wind down during March, the North Atlantic Jet stream also became less active, and moved further away from Ireland during the second half of the month. This led to a split, with the first half of March still seeing a lot of low pressure and rain, whereas the second half saw more in the way of high pressure and dry weather. Rainfall amounts ended up below average for the month overall, and temperatures also were below average.

April and May saw blocking high pressure in charge for the most part, with a weakened or split Jet stream steered away from Ireland to the north or south into the Mediterranean. This led to both April and May being very dry and mild months, with drought conditions in many places.

A pattern flip at the beginning of June pushed the blocking high pressure away, leading to an unseasonably strong Jet stream dominating our weather for the months of June and July. This has led to above average rainfall for both months, and near to, or below average temperatures.

Fig 1 – Rainfall amounts for the year so far. Note that the July data, provisionally at 122% of normal (1981-2020), is up to 29^th of July.

Outlook

High pressure building from the Azores over the weekend will work in conjunction with high pressure over Europe to break down the jet stream, introducing dry and settled conditions over the country. Rainfall amounts for the coming week will be well below average, although there is potential for some thundery downpours during the early days of next week in eastern parts of the country, which we will be monitoring closely in the coming days. Temperatures will be above average for this time of year, with maximum temperatures in the low twenties, and winds will be light.

Fig 2 – Forecast maximum temperatures across Ireland from the ECMWF model for Saturday the 8th and Sunday the 9th of August.

How does a Funnel Cloud form & Convection on 9th May 2020

Funnel Cloud Observed in Tipperary

One of the funnel cloud photos sent to us by Martin O’Brien

One of our Twitter followers, Martin O’Brien, tagged us in a series of 4 photos which clearly show a well-formed funnel cloud. He took these while passing through the scenic Blueway region in Carrick-on-Suir, Tipperary on Saturday afternoon 9th May, during this period of convection described below by Alan Hally.

Paul Downes, Forecast Meteorologist, Central Forecasts and Applications Office, Met Éireann, provided the following explanation.

This funnel, while not reaching the ground is a great example of the conservation of angular momentum. There are three main ingredients needed to get this.

Moisture. While you might not see it until it transforms into a cloud, moisture is all around us. The more humid the air the more moisture that is being suspended in the air. Saturday was a warm humid day.
Instability. Like a hot air balloon, the air inside a cloud has to be warmer than the air outside it, so when the sun heats the earth, ‘bubbles’ of warm air rises.

The air in the cools as you go up in the atmosphere, e.g. when you see ice crystals grow on the outside of an air plane window- its very cold out there! But the rate at which it cools is always changing. The air in the ‘bubble’ will cool too at a constant rate as it rises, the key here is if it cools slower than then atmosphere, we call this instability. The atmosphere is unstable and the bubble can continue to rise.

At a point called the Tropopause, approximately 10km above our heads, the atmospheric temperature begins to rise again and the air becomes stable once more. So If you have (1) moisture then as the invisible bubble rises and cools it will eventually condense into a cloud. If it is still unstable the cloud will continue to rise into a cumulonimbus (cumulus- a towering cloud, nimbus – with rain).

So that is what starts the process. The final ingredient is:

Shear. This can have several forms but for now we will just look at directional shear. If winds change direction along a front, such as a sea or lake, breeze shear can exist along the front, this can cause the air to turn. Alone it will do very little and is quite common. However if you place it under an updraft (a cloud going upwards) it acts like an ice skater in a spin. When an ice skater spins and their arms are out they rotate slowly, if they want to spin faster they pull their arms in – this is called the conservation of momentum and it works in nature just the same. If a large eddy of rotation exists along a boundary and a shower accelerated the air upward, it will tighten the rotation below it. This causes pressure to decrease and to condense, thus forming the funnel cloud we see in the photo above. In extreme cases it can produce powerful tornadoes. However more of every ingredient would be needed- which is something we rarely ever see here- as well as a lot of help from the jet stream which didn’t really play a major role on Saturday.

Convection in Ireland: Thunderstorms on Saturday the 9th of May 2020
by Alan Hally, Meteorologist in the Research, Environment and Applications Division, Met Éireann

On the 9th of May, Ireland was under the influence of a high-pressure system with temperatures in the high-teens and low to mid-twenties countrywide. Dynamically, i.e. in the highest levels of the atmosphere, there was very weak forcing due to the presence of the high-pressure. Given the location of the initial thunderstorms in the south-west, orographic forcing (i.e. upwards motion of air due to mountains) was likely a very important contributory factor to these thunderstorms. The atmospheric conditions followed a conceptual model known as “convection in fair weather conditions”. Using a combination of satellite photos and vertical cross-sections of the atmosphere, we can get a very clear picture of what was occurring on Saturday the 9th of May.

In order for a surface based thunderstorm to occur, the dew-point temperature must be 12C or higher. Figure 1 below shows a satellite photo of Ireland at 1pm on Saturday the 9th of May in the infra-red along with an overlay of the 12C dew point isotherm (in purple) from an analysis provided by the European Centre for Medium Range Weather Forecasts (ECMWF) weather model. This clearly illustrates that Munster was perfectly primed for the development of strong thunderstorms.

Figures 2 (a), (b) and (c) are what we call vertical cross-sections. These figures demonstrate respectively; rising motion (known as omega), convergence/divergence (very important for illustrating areas where thunderstorms can occur) and relative humidity. These images detail the conditions of the atmosphere from the surface up to a height of approximately 12km. Image 2 (a) displays a large area of red from approximately 1000hPa to 300hPa. This represents the very strong updrafts, or upward motions of air in the atmosphere. Images 2 (b) and (c) compliment this perfectly as they show both convergence of air at the surface (in red on 2(b)) and high values of relative humidity in the upper atmosphere (green lines on image 2 (c)). The combination of all these factors; the mountains of the south-west, the high dew-point values, the strong rising motion and the moist air in the upper atmosphere led to very heavy downpours throughout the afternoon of Saturday the 9th of May. A satellite animation of the development of the storms can be seen below in what is known as the “Day Natural Colours RGB”. The presence of tall convection producing cumulonimbus clouds can clearly be seen by the blue/cyan colours in Munster and areas over the south-east.

Figure 1: Ireland at 1pm on Sat. 9th of May in infra-red, 12C dew-point isotherm in purple

Figure 2 (a): Rising motion in red and equivalent potential temperature values in solid black lines. The equivalent potential temperature values decrease from the ground to around 500hPa, a further indication of the likelihood of convection

Figure 2 (b): Convergence of air at the surface (in red) and divergence of air higher up in the atmospshere (in blue)

Figure 2 (c): Relative humidity through a vertical layer of the atmosphere from the surface up to 200hPa. Green lines indicate values above 80% relative humidity.

Natural colours satellite image loop that shows the thunderstorms bubbling up from 06UTC to 18UTC in steps of 3-hours

Day Natural Colours RGB. The satellite image loop that shows the thunderstorms bubbling up from 06UTC to 18UTC in steps of 3-hours

Please see below thunderstorm activity, mostly over Munster this afternoon. ⛈️

Lightning strikes, when they occur, are displayed as a cross. Initially they are red but change to orange and then yellow after a period, then disappear.

For more info visit: https://t.co/YJqxvBBwTs pic.twitter.com/3ot01s5fmU

— Met Éireann (@MetEireann) May 9, 2020

Upgrade to Met Éireann’s Forecast System April/May 2020

By Dr Rónán Darcy & Dr Noel Fitzpatrick, Research Division and Evelyn Cusack, Head of Forecasting Division.
Met Éireann has launched a significant upgrade to the forecast system it uses to help predict the weather. This upgrade will aid our forecasters in their day-to-day duties and open the way to providing earlier warnings for severe weather events. The system has been developed and tested by Met Éireann staff over the past several months, and has been implemented as part of a new computing collaboration with the Dutch weather service, KNMI.

Numerical Weather Prediction (NWP) refers to the use of computer models to predict the weather, and forms the basis of modern forecasting. In recent years, national weather services and researchers have been developing and utilising an enhanced form of NWP known as Ensemble Prediction Systems (EPS).
The Met Éireann Podcast – Chaos and Computing in Weather Forecasting

While traditional weather models produce a single forecast for a given time (known as a deterministic forecast), ensemble systems produce multiple forecasts or possible outcomes for the same time period. Forecasters can then examine this range of possible forecasts to answer questions such as how likely is a given weather event (i.e. do most of the forecasts show a similar outcome or do they disagree significantly), what is the possible range of values for a weather variable like wind, temperature etc., or how much uncertainty is there in the location or timing of a storm’s arrival.

Essentially, this method marks a substantial increase in the information available to forecasters in terms of the probability of occurrence, severity and timing of given weather conditions, information that is particularly important in the build up to potentially high-impact weather events.

In 2018, Met Éireann developed its first ensemble-based NWP system, known as the Irish Regional Ensemble Prediction System (IREPS). Originally run twice per day, this system produced 11 forecasts (known as members) for weather conditions over the next 36 hours. On April 15^th 2020, the IREPS system was upgraded to a 54-hour, 11-member ensemble which is run four times per day. This will help increase how frequently our forecasters are updated on changing weather events and aid in lengthening forecast and warning times.

Technical details

KNMI Supercomputer has a capacity of 50 trillion calculations/sec (50 teraflops). HARMONIE requires around 3 quadrillion calculations

Due to the vast amounts of calculations and data that must be processed to simulate the atmosphere, large, high performance computing (HPC) systems are required to run NWP models with the necessary accuracy and timeliness. Met Éireann uses computing resources on the HPC system of the European Centre for Medium Range Weather Forecasts (ECMWF) to run its NWP models. To meet the additional computing resources required to realise the latest upgrade to IREPS, Met Éireann has established a collaboration with the Dutch national weather service, KNMI. The newly acquired resources on the KNMI HPC system have been combined with the existing resources at ECMWF, providing sufficient computing power to run the enhanced system.

IREPS is an ensemble which uses the HARMONIE-AROME model configuration (version 40h1.1) of the shared ALADIN-HIRLAM NWP system (hereafter HARMONIE-AROME). It consists of 10 ensemble members with 1 control member. The control member and the 10 ensemble members produce 54-hour forecasts and run four times daily at 00 Z, 06 Z, 12 Z, and 18 Z. IREPS runs with a horizontal grid spacing of 2.5 km, a spatial extent of 1000 x 900 grid points (see figure below), and 65 vertical levels. Both conventional (observations from weather stations, ships, buoys, balloons and aircraft) and scatterometer (satellite wind data) observations are assimilated or ingested into the model.

The geographical area over which Met Éireann runs its operational NWP forecasts is highlighted in colour.

The ensemble members are constructed using a combination of boundary condition perturbations and perturbations applied to surface parameters in the model. The boundary condition perturbations follow the Scaled Lagged Average Forecasting (SLAF) technique whereby older boundary conditions valid at the current time are perturbed by a scaling factor which depends on their age with respect to the current time. The surface perturbations are applied to a number of variables within the surface code in the model such as sea surface temperature and soil moisture. These perturbations are intended to account for uncertainty related to energy transfer from the model surface to the planetary boundary layer (usually the lowest kilometre of the atmosphere).

To summarize: The observations (initial conditions) and the model are not perfect. Small errors in the initial conditions of a forecast grow rapidly, and affect predictability. The ensembles provide forecasters with an objective way to predict the skill of a forecast and to estimate the most likely scenario. This will improve forecasts and warnings and enhance support for impact-based decision making for weather events and contribute to the safety of citizens and property.

What does output from an EPS look like?

The output of an ensemble prediction system may be displayed in many ways, each with their own purpose. Plots of all members are displayed side-by-side (called “postage stamps”) to give an indication of the spread in the range of possible solutions over a large area at a given time. In the below image, postage stamps for the 06 Z forecast from 16^th April indicate rainfall is likely to occur in the south-east, but the north east is more uncertain with some solutions suggesting relatively dry conditions.

Postage stamps from the 06 Z IREPS on 16th April 2020 showing rainfall predicted up to 54 hours later – between 09 Z (10:00 local) and 12 Z (13:00 local) on the 18th April 2020. All eleven members (1 control + 10 perturbed) are plotted, as well as their mean.

Another method combines all members together to form a single pseudo-probability plot based on a threshold. In the image below, the number of members exceeding 5 mm of rainfall in 6 hours are counted, giving an indication of the probability of this threshold being exceeded over the area plotted.

A pseudo-probability plot for rainfall totals exceeding 5 mm in a 6 hour window. The raw data has been upscaled to 5x5 grid points to avoid the double-penalty issue seen with high-resolution ensemble prediction systems.

A pseudo-probability plot for rainfall totals exceeding 5 mm in a 6 hour window. The raw data has been upscaled to 5×5 grid points to avoid the double-penalty issue seen with high-resolution ensemble prediction systems.

Yet another method is the use of meteograms. Here, a time-series plot is produced for a specific parameter at a single location to visualise how each of the ensemble members progress. This gives an indication of the spread, and identifies “clustering”, where several members may bunch around a particular solution.

A meteogram time-series plot demonstrating the evolution of the temperature forecast at Dublin Airport for each of the 11 members of an IREPS forecast

Case Study 1: Ophelia Monday 16th October 2018

Prior to Ophelia only the deterministic forecast (a) was available from HARMONIE-AROME. The track of Ophelia was re-run using the 10-member ensemble system (b). While the deterministic track was very close to the observed track, had the IREPS been available 54-hours ahead it would have given more certainty to the forecasters particularly helping to provide a longer lead-in time in the issuing of the Status Red wind warnings.

(a) Projected track of the central low pressure of Ophelia over a 24-hour period from the operational run of HARMONIE-AROME at 0000 UTC on the 16th of October.
(b) Projected track of the central low pressure of Ophelia over the same period for each of the ensemble members of IREPS – this illustrates the confidence we could have in the track of Ophelia.

Case Study 2: Thunderstorms, Saturday 9th May 2020

Saturday the 9^th May 2020 was a warm, humid day with temperatures up to 24 degrees. Thunderstorms with hail developed in the afternoon. The white map of Ireland is the afternoon radar on the 9^th showing intense showers/thunderstorms. The other 11 green maps are the showers as forecast by our new 54-hour IREPS from a forecast on the evening of Thursday the 7^th, each one being a possible outcome.

The overall IREPS forecast was excellent. However the 10 ensemble members show the different locations possible illustrating how difficult it is to pinpoint exactly where showers will develop and how difficult it still is to give thunderstorm warnings for exact locations two days ahead.

Some cumulus congestus on their way to becoming cumulonimbus thunderstorms at Thurles, Co Tipperary Saturday morning, 9th May. Photo by Dr Emily Gleeson, Research scientist Met Éireann.

You can listen to Rónán Darcy and Alan Hally talking about setting up IREPS and its benefits for weather forecasting.

Further plans to 2023

Met Éireann’s operational NWP team from top left; Colm Clancy, Rónán Darcy, Alan Hally and below, NWP team leader, Eoin Whelan

The upgrade to IREPS is thanks to the development of the system by our Met Éireann NWP team led by Eoin Whelan and the substantial installation and testing work performed by them over the last several months. In addition, personnel from Technology, Forecasting, and Business Services Division were involved in testing and implementing the necessary technical changes and in managing the agreements and approvals required for our collaboration with KNMI.

The next stage in Met Éireann’s HPC projects will see us collaborate with Denmark, Iceland, and the Netherlands to develop a common numerical weather prediction system. Known as UWC-West, this project is due to go operational in 2023 and preparations are well underway with most non-shift staff in Met Éireann remote working at this time.

An Update on Rainfall, Pollen and UV

by Gavin Gallagher, Meteorologist, Met Éireann

An Update on Recent Rainfall Measurements and the Rainfall Forecast, Recent Drought conditions, Pollen & Sunburn.

Low Rainfall levels for March and thus far in April have brought drought and an increased risk of forest fires.

The majority of monthly rainfall recordings across the country were below their Long-Term Average for the month of March, as high pressure dominated our weather from mid-month. The lowest relative rainfall being 56% of the expected monthly rainfall at Moore Park, Co Cork, with a monthly rainfall total of just 47.9 mm.

The much drier than normal weather from the midpoint of March to mid-April has led to meteorological ‘Dry Spells’ and ‘Absolute Drought’ conditions in parts of Ireland. A dry spell is defined as “A period of 15 or more consecutive days to none of which is credited 1.0 mm of precipitation”, while absolute drought conditions in Ireland are defined as “A period of 15 or more consecutive days to none of which is credited 0.2 mm or more of precipitation.”

Recent Dry spells have been recorded at the following stations:

Absolute drought has recently been recorded at the following stations:

Above is the recorded rainfall for Dublin Airport for the month of March. The green line is the long term average (or expected) rainfall. The red lines are the daily rainfall amounts, with blue being the cumulative rainfall. Note the near zero rainfall from mid-March.

Find the graph for your local area here:

https://www.met.ie/climate/past-weather-statements

Choose “Rainfall Graph” from the menu.

Above is the cumulative rainfall for Athenry in Co. Galway for the past 20 days. The pink line is the long term average (or expected) rainfall, the blue line is the actual amount received and the light blue/green lines is the range of rainfall forecast (from our model ensemble) over the next 10 days. This shows that rainfall is well below expected values and will remain so for the coming 10 days.

Past 7 Days Rainfall:

Rainfall totals were below average across the entire country in the past week. Largest relative totals of up to 86% of normal were measured in inland parts of southern Leinster, however most areas received only 10 to 50% of average rainfall for this time of year, mainly resulting from rainfall last Sunday, April 5th.

Forecast Rainfall (Fri April 10 to Fri April 17) :

Areas in the west and north of the country will receive rainfall today, Friday, and again tomorrow Saturday, while it will remain mostly dry elsewhere. All areas will likely see rainfall on Sunday, before high pressure dominates our weather again from early next week, heralding another period of mostly settled, mostly dry weather.

Below, is the forecast rainfall (mm) for the next 7 days out to midday Friday April 17^th. Most of this rain will fall this Sunday April 12^th.

The longer range forecast for late April and early May is for our weather to be drier than normal with below average rainfall.

It is worth noting that with rainfall below average, the danger of forest fires / gorse fires burning out of control, increases

U.V.

As we approach the midpoint of spring, the sunlight we receive becomes noticeably stronger, with harmful UV rays causing sunburn. People may be surprised to get sunburn in early April, but it’s helpful to remember that the sun is as strong in Ireland in April as it is in August. Sunlight is at its strongest at the summer solstice in June, then it is as strong in May as it is in July, as strong in April as it is in August and so on. So even though it may not be as warm in April as in August, the sun is just as strong, and you will still burn when exposed to the sun.

Also, the ozone hole over the Arctic is at its biggest (most damaging) at the end of winter and during spring, allowing more harmful UV rays to reach the surface.

Below, is the UV measurement from one of our Brewer Spectrophotometers (an instrument which measures ozone, and computes the UV level). This one is at Valentia Observatory in Co. Kerry, and the UV Index today is low due to cloud cover.

Daily U.V. forecasts will be issued by Met Éireann and be available on our website and social media from Tuesday April 14^th.

Pollen:

Tree pollen peaks in Ireland in March and April with grass pollen at its peak from May to August. Daily pollen forecasts will be issued by Met Éireann and be available on our website and social media from Tuesday April 14^th.

World Meteorological Day - 23rd March 2020

by Joanne Walker, Met.ie website/app manager, Digital Communications Unit, Forecast Division

This year it focuses on Climate and Water

World Meteorological Day showcases the essential contribution of National Meteorological and Hydrological Services to the safety and wellbeing of society. This work continues 24/7 despite the challenges and constraints of the pandemic.

“We feel the effects of climate change mostly through water: more floods, more droughts, more pollution. Just like viruses, these climate and water-related shocks respect no natural boundaries,” said WMO Secretary-General Petteri Taalas.

”The world needs to demonstrate the same unity and commitment to climate action and cutting greenhouse gas emissions as to containing the Coronavirus pandemic,” he said.

“Changes in the global distribution of rainfall are having a major impact in many countries. Sea levels are rising at an increasing pace, driven by melting of the largest glaciers, like in Greenland and Antarctica. This is exposing coastal areas and islands to a greater risk of flooding and the submersion of low-lying areas,” said Mr Taalas.

Taken from the WMO World Met Day 2020 press release, available here.

This week our Met Éireann app will be updated allowing you to set up and receive Push Notifications of all Marine Warnings for Ireland.
Met Éireann provide climate information services which promote the safety of citizens and supports economic and environmental resilience.
Met Éireann is developing a Flood Forecasting Warning Service in conjunction with the OPW.

Weather is so much a part of our everyday life that access to high quality information on the weather is expected or taken for granted as a normal convenience of modern life — whether it’s a storm or a flood that threatens life and property, fog or icy conditions that disrupt road transport or air traffic, or just a minor inconvenience due to summer showers. The changing climate and, the increased frequency of extreme weather events, in tandem with increased urbanisation, is making Ireland more vulnerable to the impacts of weather. Since our beginnings over 80 years ago Met Éireann has been serving Ireland by providing public weather information, forecasts and warnings to help protect life and property. Over the next decade we will rise to the growing challenges of climate change by supporting Ireland in becoming weather and climate prepared.

Marine Services

Met Éireann produces specialised sea area forecasts for Irish coastal waters and inland lakes, and our wave height forecast map. We work closely with the Coastguard and other agencies in the protection of life and property. Met Éireann has produced a number of reports into how climate change will affect water levels around the coasts.

Our Marine Climatology page contains graphs of buoy data since they were installed and the record of average monthly sea temperatures at Malin Head compared with the WMO 30 year average period of 1961-1990.

We are currently developing a Flood Forecast Centre with the OPW to assist the public and the emergency services in preparing for major flood events.

Met Éireann actively promotes Water Safety particularly during the key summer months with a permanent link on our homepage to Water Safety Ireland and our Water Safety information and advise article.

: Marine Forecasts on our app

: Wave forecast map

: Average monthly sea temperatures at Malin Head compared to the 30 year average. 2018 – 2019

Climate Services

Air Masses

In the Climate menu of our website you can learn all about the Climate of Ireland, read up on our work on Climate Change, view the Weather Extreme Records for Ireland and download reports on Major Weather Events in Ireland.

The Past Weather Statements page contains a vast archive of monthly, seasonal and annual weather summaries along with daily values and rainfall, temperature graphs.

Our Climate Services are focused on the timely production and provision of high quality data (observational data, gridded data, scientific analysis, etc) and products to decision makers. In order to support Irish society at large and facilitate the development and evaluation of adaptation and mitigation strategies for Ireland.

Oak Park Weather Station, Carlow

Our Available Data section contains graphs of Daily Data and Monthly Data from all our weather stations, you can also download Historical Data from those stations and our voluntary observer stations. Read all about MÉRA- our Climate Re-Anaysis project, and view the 30 Year Averages- the WMO recommend that climate averages are computed over a 30 year period of consecutive records.

What does a weather station look like? Photos and details of all our weather stations- and webcams images- are available here.

View the archive of Lightning strikes over Ireland on a map, download available.

WOW-IE

WOW-IE map

WOW-IE is the Weather Observations Website of Met Éireann and is part of the global WOW network of crowdsourced weather observations. It is available at wow.met.ie If you own a weather station we invite you to connect it to the WOW database and view the data online. You can view real-time temperature, pressure, wind values and more from privately-owned weather stations, Met Éireann’s stations (including half hour observations) and from National Meteorological Services around the world!

WOW-IE is a Weather Education and Data Comparison tool. You can view the archive of past weather observations on the WOW-ie map, on a graph or table and the data is available to download. WOW-IE displays weather observations from various sources in real-time*.

WOW-IE uses the UK Met Office WOW database, as do national meteorological services in the Netherlands, Belgium, Sweden, New Zealand and Australia whose data can also be viewed on the WOW-IE map. Currently in Ireland there are about 15 private weather station owners uploading their weather observations to WOW-IE. Met Éireann uploads data from 20 of its official automatic weather stations and over 30 of its new automatic climate stations. By sharing your weather station data you are helping to improve the Irish weather observing network and helping Met Éireann forecasters to get a better picture of weather around Ireland.

*Met Éireann does not correct or review WOW data, hence incorrect values or missing data may occur, even from official stations. Quality controlled data from Met Éireann’s official weather stations are available here.

Image from Met Éireann's strategy statement

Click to view Met Éireann’s strategy statement

Storm Jorge – Saturday 29th February 2020

Storm Jorge from Space – Saturday 29th of Feb, 2020

By Conor Lally (Meteorologist, Observations Division)

Presented are a series of three satellite images detailing the progression of Storm Jorge (pronounced Hor-hay), the seventh winter storm of the season, as it crossed the country today.

These images are Natural Colour RGB (Red Green Blue) composites courtesy of the European Organisation for the Exploitation of Meteorological Satellites (EUMETSAT). Composite satellite images combine pictures taken at different visible and infra-red frequencies, each of which contains slightly different information. To highlight each picture’s own particular specialty, that is to say those features that are captured best in that particular frequency, they are tinted a different colour. Then when combined together they reveal more information than they would by themselves.

The centre of the storm Jorge, which developed in the mid-Atlantic and deepened rapidly as it approached Ireland thanks to a strong jet stream aloft, was clearly identifiable as the dark patch to the west of the country in the first of our series of satellite photos, which was taken at 9am. At this stage the pressure in the centre of the storm was predicted to be in the region of 950 hPa and the closest of our stations to the centre of the storm, Belmullet in Co Mayo, recorded a Mean Sea Level pressure of 963 hPa.

Despite the proximity of the storm centre we can also see that Saturday started off as a bright clear day for many with an absence of cloud for much of the eastern half of the country. However, the storm quickly began make its presence felt shortly after sunrise on the west coast, as a swathe of storm force winds began to drive in across the west of the country by which time our station in Mace Head had already recorded a wind gust of 92 km/hr.

We can see in the second image taken at 11 pm the storm’s occluded front, which was visible as the thick band of cloud in the shape of a comma head that is wrapped around the storm’s centre, push its way into to the middle of the country. With the front came heavy rain but also for a short while some sleet and snow along its leading edge. Our station in Knock airport recording 3 cm of snow lying by 11 am. Looking carefully at our composite image we can just discern this band of frozen precipitation as a light blue streak to the right of the thick white and warmer cloud of the front. The tip of the comma head often contains much of the highest winds and this is evident in the winds recorded at this time with Mace Head, Newport, and Athenry recording gusts of 133, 102 and 98 km/hr.

In our third image taken at 1 pm, the front has spread across the whole of the country and ‘Jorge’ now shows signs of a maturing system. What was in our first image the tight core of the storm centre has become elongated as cold air, visible in the picture as the dark clear sector east and south of Ireland, was dragged into the centre. This has the effect of cutting the storm off from the supply of warm air which drives it and thus reducing its intensity.

Table listing the highest ten minute means and gusts observations for each of the weather stations

Storm Jorge: highest ten minute means and gusts

Meteorologist’s commentary issued at 6pm Thursday 27^th February 2020

by Joan Blackburn (Deputy Head of Forecasting Division), Sinéad Duffy (Meteorologist, Technology Division) and Eoin Sherlock (Head of Flood Forecast Division) on Thursday, 27^th February 2020

Storm Jorge (named by AEMET, the Spanish meteorological service) is the latest in a series of Atlantic storms this month and is due to affect Ireland from early Saturday. Rain will extend countrywide from the west tonight, before the storm arrives.

The Meteorological Situation:

Storm Jorge (pronounced Hor-hay) is a storm centre which will undergo rapid cyclogenesis in the mid-Atlantic during Friday 28th February as it tracks northeastwards towards Ireland. It is then expected to fill slowly as it crosses over the north of the country during Saturday 29^th February. Figure 1 shows the forecast position of Storm Jorge and its associated fronts at 12 midday on Saturday.

Figure 1. Forecasted position and fronts of Storm Jorge at midday Saturday 29th February.

Storm Jorge is forecast to bring severe winds to western and northwestern coastal counties (orange wind warning) and less severe winds to the rest of the country (yellow wind warning) from Saturday morning into early Sunday morning.

Spells of heavy rain associated with Storm Jorge will worsen the flooding situation across the country. A yellow level rainfall warning will come into operation for Munster, Connacht and Donegal from tonight (Thursday night) to late on Saturday evening.

The animation in figure 2 below shows the position of the strong Atlantic jet with the corresponding deepening of the storm centre from early Friday morning to early Sunday morning.

Figure 2. Forecast position of the Jet stream during Storm Jorge

Figure 3 shows the wind field from the Harmonie high-resolution weather model for early Saturday morning, the start of the orange warning for Mayo, Galway, Clare and Kerry.

Figure 3. Wind warning forecast from the Harmonie weather model at 6am Saturday 29th February

Storm Jorge is the seventh named storm of the season. It was originally named by AEMET, the Spanish national meteorological service, due to the impact of the storm’s active cold front which is forecast to bring severe gusts and strong waves to the northwest of Spain.

Here’s the list of the winter storms so far this season:

Lorenzo, 4^–Oct-2019 (Ex-hurricane, named by the NOAA National Hurricane Centre in the USA)
Atiyah, 8-Dec-2019
Elsa, 18-Dec-2019 (named by IPMA, the national meteorological service of Portugal)
Brendan, 13-Jan-2020
Ciara, 9-Feb-2020
Dennis, 16-Feb-2020
Jorge, 29-Feb-2020 (named by AEMET, the national meteorological service of Spain)

Storms are named to aid the communication of approaching severe weather, helping the public to be better placed to keep themselves, their property and businesses safe. Met Éireann are part of a western Europe storm-naming group which includes the Dutch meteorological service, KNMI and the UK’s meteorological service UKMO. The national meteorological services of Spain, Portugal, France (MeteoFrance) and Belgium (RMI) are part of a southwestern Europe storm-naming group which has a separate list of names allocated to the Winter 2019/20 storm season. When a storm has already been officially named by another national meteorological service or the US National Hurricane Centre, that storm name is retained.

Flooding issues

A) Elevated river levels
Currently river levels are elevated across the country, particularly in the Midlands (Shannon catchment). Levels across the Northern half of the country are also high. Therefore, additional rainfall over the coming days will compound the flooding issues here.
B) Coastal Flooding
We are in a period of transition between Spring (High) Tides and Neap (Low) Tides. This means there will not be a large variation between high and low tides. The combination of high seas and strong winds or stormy conditions associated with Storm Jorge may increase the possibility of coastal flooding, especially in flood-prone areas along the Atlantic coast on Saturday (particularly when coincident with high tides).

Keep up to date

As forecast confidence improves over the coming days Met Éireann will issue warnings as required. Please check for updates on https://www.met.ie/warnings.

Push notifications for all weather warning levels (yellow, orange and red) for your location are available on the latest version of the Met Éireann App.

February’s Rainfall Accumulations

Latest February Analysis 2020 updated at 10am, Wednesday 27th February 2020 by Paul Moore, Aidan Murphy and Sandra Spillane, Climate Services

A strong Stratospheric Polar Vortex, coupled with the troposphere, has led to the North Atlantic Oscillation being in a strongly positive phase during February 2020. This has resulted in a zonal pattern across the Atlantic with a strong Polar Jetstream, further south than normal, bringing a series of vigorous Atlantic depressions, towards or just to the north of Ireland. These depressions, including two named storms, Ciara and Dennis, brought prolonged periods of heavy rainfall and stormy weather leading to extensive flooding in places, particularly along the Shannon catchment. Heavy rainfall falling on already saturated ground and with low evaporation rates in winter exacerbated the flooding.
The position and strength of the Polar Jetstream has resulted in 1.5 to 3 times the normal monthly rainfall so far for February throughout the country (a month usually associated with one of the least rainfall amounts).
The highest monthly rainfall total during the period 1-26 February was observed at Newport, Co Mayo with 306.6 mm (242 % of its February LTA). The Lowest monthly rainfall total during the period 1-26 February was observed at Dublin Airport, Co Dublin with 120.7 mm (247% of its February LTA). While the highest daily rainfall total was 51.5 mm on Saturday 8 February 2020 at Knock Airport, Co Mayo (50% of its monthly LTA).

So far this month, ten synoptic stations have already had their wettest February on record, including Phoenix Park, Co Dublin (records going back to 1850), Shannon Airport, Co Clare (record length 74 years), Newport, Co Mayo (record length 60 years), Claremorris, Co Mayo (record length 19 years), Casement, Co Dublin (record length 56 years) and Knock Airport (record length 23 years).

Full report <<here>>

Meteorologist’s Commentary at 12 noon, Monday, 25^th February 2020 by Sandra Spillane PhD, Climatologist and Aidan Murphy, Climate Services

The Weather and Climate Statements for February 2020 and Meteorological Winter 2020 (December 2019, January 2020 and February 2020) will be published on the 2nd working day and 3rd working day of March 2020 respectively. For these publications, and more, see: www.met.ie/climate/past-weather-statements.

The recent rainfall is above average at all our SYNOPTIC stations when compared to the 1981-2010 climatological long-term-average period (LTA, the World Meteorological Organisation’s standard period range for weather comparisons). The provisional rainfall totals for 1-24 February are currently at 225% of Ireland’s average. For comparison, December 2015 (Storms Desmond on Sat 5th, Eva on Thu 24th and Frank Tue 29th), was around 245% of normal.

Note: the provisional value may go up or down by the end of the month, as quality control is completed on the data and as more rainfall observations come into Met Éireann. You might spot in the February 2020 maps below that there are gaps in mountain regions, the reason for this is due to their location and that rainfall totals at mountain stations are generally read once a month.

A series of vigorous Atlantic depressions affected the country in February, tracking closer to Ireland than usual and bringing prolonged periods of heavy rainfall and stormy weather leading to extensive flooding in places. The Polar jet stream extended across the Atlantic right over Ireland for most of the month, marking the tracks of successive storms resulting in 1.5 to 2.5 times the normal rainfall so far this month throughout the country.

The highest monthly rainfall total during the period 1-24 February was observed at Newport, Co Mayo with 283.5 mm (224% of its LTA). While the highest daily rainfall total was 51.5 mm on Saturday 8 February 2020 at Knock Airport, Co Mayo (50% of its monthly LTA).

Be aware of flooding and keep up to date with the latest warnings and weather forecasts for your area: www.met.ie/warnings.

The following graph illustrates Newport’s cumulative daily rainfall graph for the last 20 days together with the Forecast Ensembles going into the coming week.

It is not unusual for a single highest monthly total rainfall accumulation to be in this range and higher.

Recent Highest February Rainfall Totals

2019: 569.9 mm at in the Cummeragh Mountains (gauge no.3), Co Kerry (216% of its LTA), 81.9 mm on Tuesday 19 February 2019 at this station
2018: 305.9 mm at in the Cummeragh Mountains (gauge no.3), Co Kerry (116% of its LTA)
2017: 400.1 mm at Beenreagh Mountains, Co Kerry (164% of its LTA)
2016: 550.0 mm at Beenreagh Mountains, Co Kerry (225% of its LTA) with 99.5 mm on Tuesday 16 February (41% of its monthly LTA)

What is unusual is the lowest monthly rainfall total, observed at a rainfall station, to be this high. During the period 1-24 February 2020 at Roches Point, Co Cork there has been 115.7 mm total rainfall, this value is 155% of its monthly LTA (result is provisional until quality control is completed). The following graph illustrates Roches Point’s cumulative daily rainfall graph for the last 20 days together with the Forecast Ensembles going into the coming week.

Recent Lowest February Rainfall Totals

2019: 15.8 mm at Ringsend, Co Dublin (37% of its LTA)
2018: 19.0 mm at Ringsend, Co Dublin (44% of its LTA)
2017: 28.5 mm at Clogher Head (Port), Co Louth (54% of its LTA)
2016: 43.6 mm at Malahide Castle, Co Dublin (100% of its LTA)

The following maps are for (provisional) 1-24 February 2020 and December 2015 when up to 943.5 mm of rainfall fell at Gernapeka, Co Cork. The lowest during that month was 149.0 mm at Malahide Castle, Co Dublin (219% of its LTA).

The following gridded maps show the observed rainfall totals across the last four February’s for comparison.

Feb 2016	Feb 2017	Feb 2018	Feb 2019

To read more on the national weather records, see www.met.ie/climate/weather-extreme-records.

Storm Dennis – Saturday 15th to Monday 17th February 2020

Latest updated Meteorologist’s Commentary issued at 3pm, Friday, 14^th February 2020 by Paul Downes, Meteorologist, Forecast Division

Storm Dennis – Saturday 15^th to Monday 17^th February

Storm Dennis (as named by the UK Met Office), is currently undergoing rapid cyclogenesis in the western Atlantic. While staying to the northwest of Ireland, Storm Dennis will produce some wet and windy weather over Ireland this weekend.

The Meteorological Situation (Technical Discussion)

The strength of the jet stream is determined by the temperature gradient closer to the surface. We call the zone where warm and cold air meet the baroclinic zone (a strong temperature gradient that separates warmer air from colder air and often the battle field that spans our storms).

The ongoing battle between warm air over the south central Atlantic and a cold pool over much of eastern Canada has led to a strong level baroclinic zone fuelling a powerful jet aloft with several waves tracking across the Atlantic. The lead wave has been the driving force for this first deep low (~933 hPa) currently tracking in a northwesterly direction and occluding south of Iceland.

Warm air being pushed up along the US east coast meeting very cold air over Eastern Canada is the driving force for this powerful jet, with winds up to 225 knots (~416 km/h) at its core, currently aiding the rapid development of Storm Dennis. Dennis will develop rapidly today. Rapid cyclogenesis is defined as a drop in pressure of greater than 24 hPa in 24 hours. This storm is forecast to drop by around 70 hPa in 24 hours as it rapidly tracks north towards Iceland. With a forecast central pressure in the low 9-teens it will rival the lowest recorded pressure in the north Atlantic of 914 hPa, which occurred off the coast of Scotland on Monday 11th January 1993. The core of Storm Dennis is expected to stay well to our northwest as it rapidly strengthens, before pirouetting (the Fujiwhara effect) around Friday’s low and coming back to visit us on Sunday as it slowly weakens.

View the Atlantic air mass chart animation here

Timeline for Ireland

For the latest warnings see: www.met.ie/warnings

Saturday: The first round of wet and windy weather will reach the Atlantic coast on Saturday morning spreading countrywide during the morning easing later and Status Yellow wind and rain warnings are in operation.

Sunday: The core of storm Dennis (actually a hybrid of Friday’s low and Storm Dennis) will gradually fill and weaken as it tracks south-eastward towards Ireland bringing squally showers with a risk of thunder. A widespread status Yellow wind warning is likely to be issued and possibly Orange level winds locally (especially in the vicinity of squally showers along Atlantic coasts) can be expected.

Monday: Winds will gradually ease through Monday, but not dissimilar to this past Monday showery conditions can be expected with wintry conditions possible.

Flooding issues

A) Elevated river levels
Currently river levels are elevated across the country, particularly in the midlands, west and south, so any heavy rainfall would cause issues

B) Coastal Flooding
We are entering into a period of transition between Spring (High) Tides and Neap (Low) Tides. This means there will not be a large variation between high and low tides. The combination of high seas and strong winds or stormy conditions, may increase the possibility of coastal flooding especially along western and southern coasts Saturday and Sunday coinciding with high tides.

As forecast confidence improves over the coming days Met Éireann will issue warnings as required. Please check for updates on https://www.met.ie/warnings.

Meteorologist’s Commentary issued at 5 pm, Friday 14^th February 2020 by Sandra Spillane PhD, Climatologist

Historic low pressures

During the storm called the ‘Night of the Big Wind’, barometric pressure was estimated to be as low as 918 hPa on 6 January 1839. It was the worst storm to affect Ireland for 300 years. It is also considered to have one of the lowest core pressures ever been recorded near the Irish isles.

“The two lowest barometric readings recorded in the Atlantic Ocean have occurred in the eighties and nineties of the 20th century. The first was the Atlantic Cyclone of 15 December 1986, which deepened to 916 hPa, and the other was the storm of 10-11 January 1993 which is much better documented. According to Gulev et al. (2001), Northern Hemisphere winter cyclones have intensified and produced deeper central mean sea level pressures in recent decades. However, these winter cyclones also appear to have shorter life cycles and dissipate more quickly.”

Source: http://oiswww.eumetsat.org/WEBOPS/iotm/iotm/19930111_storm/19930111_storm.html

Deep Atlantic lows, of course, may not come close to Ireland. The five lowest mean sea level pressure (MSLP) observations in the National Climate Archive are:

Date	Station location	MSLP (hPa)	Station Pressure (hPa)
Sun 4 Feb 1951	Middleton, Co Cork	942.3	941.2
Sun 17 Dec 1989	Cork Airport, Co Cork	942.8	924.5
Sat 16 Dec 1989	Valentia Observatory, Co Kerry	943.0	941.4
Tue 17 Jan 1995	Belmullet, Co Mayo	943.2	942.1
Thu 1 Dec 1966	Malin Head, Co Donegal	943.6	940.7

February’s lowest mean sea level air pressures

The lowest February hourly mean sea level pressure observed at an Irish land station was 942.3 hPa at Middleton, Co Cork on Sunday 4 February 1951. The highest sustained (10-minute mean) wind speeds observed on that date was 65 km/h (35 knots, Gale Force) at Shannon Airport, Co Clare, while the highest gust (3-second mean) wind speed was 107 km/h (58 knots) at Valentia Observatory, Co Kerry during the evening. The highest 24 hour rainfall amounts around this event was:

67.6 mm at Waterville, Co Kerry on Saturday 3rd
51.3 mm at Rathdrum, Co Wicklow on Sunday 4th
39.4 mm at Mountrath, Co Laois on Monday 5th

For more on the storm Night of the Big Wind, see www.met.ie/cms/assets/uploads/2017/08/Jan1839_Storm.pdf.

For the national records of mean sea level pressure, see https://www.met.ie/climate/weather-extreme-records.

Meteorologist’s Commentary issued by Dr Rónán Darcy, Meteorologist, Research Division on Wednesday 12th February 2020.

Storm Dennis – Saturday 15^th to Monday 17^th February 2020

Storm Dennis is forecast to track to the north of Ireland and the UK over the weekend. It will likely bring periods of very wet and windy weather, with some stormy conditions possible, particularly later Sunday into Monday.

The Meteorological Situation:

Cold air is forecast to exit Canada and enter the North Atlantic Ocean over the next few days, creating a sharp temperature gradient in the atmosphere. This will result in an intensification of the jet stream, shown in the graphics below, which will direct low pressure systems towards Ireland.

Gales are likely in coastal areas on Saturday with fresh to strong winds inland. Winds could increase further on Sunday, possibly becoming stormy, particularly along western coasts. It will be very gusty too over the weekend, with some damaging gusts possible.

Flooding issues

We are entering into a period of transition between Spring (High) Tides and Neap (Low) Tides. This means there will not be a large variation between high and low tides. The combination of high seas and strong winds or perhaps stormy conditions, may increase the possibility of coastal flooding especially along western and southern coasts due to wave transformation.

Storm Dennis may also bring very wet conditions with localised flooding possible. River levels are elevated across much of the midlands so any heavy rainfall would cause issues here.

Storm Naming

Storm Dennis is the fourth named storm of the season. The naming convention now also includes the Dutch meteorological service, KNMI as well as our existing partner UKMO. Storms are named to aid the communication of approaching severe weather, helping the public to be better placed to keep themselves, their property and businesses safe.

Keep up to date

As forecast confidence improves over the coming days Met Éireann will issue warnings as required. Please check for updates on https://www.met.ie/warnings.

Weather Warning Alerting Services

Push notifications for all weather warning levels (yellow, orange and red) for your location are available on the latest version of the Met Éireann App. Alternatively, you can also sign up to receive emails/SMS (red only) of weather warnings on our warning page. Both services are outlined here.

Storm Ciara - Sunday 9th February 2020

UPDATE

Issued 13:00, Saturday, 8th February 2020, by Evelyn Cusack, Head of Forecast Division and Eoin Sherlock, Head of Flood Forecast Division.

Storm Ciara will pass to the north of Ireland on Sunday. It will bring extremely windy and in places stormy conditions during the morning. Southwest winds will reach gale to strong gale force in strength with damaging gusts likely.

These gusts will affect parts of the country not normally impacted by such strong winds. Gusts will typically range between 100-130 km/h but they may exceed 140 km/h locally ( see animation below).

Orange wind warnings have been issued for Storm Ciara. For full warning information please see https://www.met.ie/warnings

Flooding Issues:

We are in a period of Spring Tides and these will coincide with very high seas which will start today Saturday and will continue into next week.

The combination of Spring Tides, high seas and extremely strong winds or stormy conditions will result in a significant risk of coastal flooding especially along northwestern and western coasts. This risk will persist into the middle of the coming week.

Storm Ciara will also bring very wet conditions with localised flooding possible as intense falls of rain spread across the country with some embedded thunderstorm activity.

Wintry weather

As Storm Ciara moves away on Sunday colder air is introduced over Ireland. This will bring scattered wintry precipitation later on Sunday night. The risk of snowfall increases as we move into the coming week. While snow showers may occur anywhere they will occur chiefly in parts of the north and west.

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UPDATE

Issued 15:00, Friday, 7th February 2020, by Evelyn Cusack, Head of Forecast Division and Eoin Sherlock, Head of Flood Forecast Division.

Storm Ciara is expected to pass to the north of Ireland on Sunday but the country can expect some wet and windy weather before this on Saturday.

This spell of weather will bring heavy rain and strong winds, which have the potential to cause some disruption especially in western and northern counties.

The animation below displays the forecast winds for Saturday, 8th February using the Harmonie Forecast model.

As well as the heavy rain and strong winds, there is the risk of coastal and localised flooding.

As we get closer to a weather event Met Éireann’s high resolution model Harmonie allows us to enhance the level of detail in our forecasts.

Met Éireann has this afternoon increased the wind warning levels for Saturday to Orange for Galway, Mayo and Donegal.

For the most up to date warnings please click here (https://www.met.ie/warnings):

Flooding Issues:

We are entering a period of Spring Tides and these will coincide with very high seas which will start on Saturday and will continue into next week.

The combination of Spring Tides, high seas and extremely strong winds or stormy conditions will result in an elevated risk of coastal flooding especially along north western, western and southern coasts. This risk will persist into the middle of next week.

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Issued 15:00, Wednesday, 5th February, 2020, by Matthew Martin, Meteorologist, Forecast Division; Evelyn Cusack, Head of Forecasting and Eoin Sherlock, Head of Flood Forecast Division

Lá Fhéile Bríde

The first of February, marks the first day of spring in the Gaelic Calendar. The days are getting noticeably longer (dawn is an average of one to two minutes earlier in the morning and sunset one to two minutes later every evening). But in the Meteorological Calendar, which is based on average temperatures, February is the third month of winter and we can get very severe weather with the full winter range possible from heavy rain and floods to damaging wind storms, and also of course snow and ice.

Storm Ciara

Unsettled weather is expected to develop across Ireland and Northwest Europe this weekend. The change will occur as very cold air sweeps out of Canada into the North Atlantic creating a sharp temperature contrast in the atmosphere over the ocean. This temperature contrast will result in the intensification of the jet stream over the North Atlantic, which will drive vigorous areas of low pressure towards Ireland.

The animation below shows the evolution of the jet stream over the coming days.

After a period of rather quiet weather, the change to unsettled mobile conditions will occur during Friday (7^th Feb) as wet and windy weather moves in from the Atlantic. A further spell of heavy rain is expected on Saturday (8^th Feb) and this will be accompanied by strong and gusty winds with a possibility of Status Yellow warnings.

Weather conditions are expected to deteriorate further on Sunday (9^th Feb) as Storm Ciara (named by the UK Met Office on Wednesday 5th February) tracks to the north of Ireland.

Storm Ciara is forecast to be a vigorous Atlantic storm system with an expansive wind-field. Numerical Weather Prediction Models project the centre of the storm to track close to northern Scotland with a minimum central pressure of around 940hPa at lunchtime Sunday (see Figure Below).

There is a growing consensus that Sunday will be an extremely windy day across Ireland and the UK with widespread heavy rain, squally showers and with gales or storm force winds around our coasts.

Storm Ciara is the third named storm of the season. The naming convention now also includes the Dutch meteorological service, KNMI as well as our existing partner UKMO. Storms are named to aid the communication of approaching severe weather, helping the public to be better placed to keep themselves, their property and businesses safe.

Next week, conditions will remain very disturbed across Ireland and the UK. It will remain very windy and turn much colder with the chance of wintry showers and ice in some parts.

Flooding issues

The country will enter a period of Spring Tides this weekend. This will coincide with high seas, which are likely to affect coastal areas at first on Saturday but will continue into Sunday and the early days of next week. The combination of high Spring Tides and high seas as well as extremely windy or stormy conditions later in the weekend and early next week will result in an elevated risk of coastal flooding especially along western and southern coasts.

The unsettled weather is likely to produce significant rainfall totals over the weekend. This will result in an increase in river levels and may cause some localised flooding.

Keep up to date

As forecast confidence improves over the coming days Met Eireann will issue warnings as required. Please check for updates on https://www.met.ie/warnings.

Push notifications for all weather warning levels (yellow, orange and red) for your location are available on the latest version of the Met Éireann App.