Information to follow was included by Meteorologist Liz Walsh on Thursday 10th January 2019
What is Sudden Stratospheric Warming?
The earth’s atmosphere is comprised of layers based on temperature. We live in the lowest part of the atmosphere – the troposphere – which contains most of our weather – clouds and precipitation – and on average it’s about 10 km deep, although the depth does vary from the equator to the poles – greater at the equator, lesser at the poles. The Jet Stream is at the top of the troposphere and most of our weather happens below that.
Above the troposphere is the stratosphere and this layer of the atmosphere extends upwards to about 50km. It contains much of the ozone in the atmosphere which absorbs all the ultra violet rays from the sun causing it to warm up. Temperatures in the stratosphere are generally highest over the Summer Pole where the sun shines all day and night and, conversely, lowest over the Winter Pole. So in winter the stratosphere is usually very cold at the pole and this is what the Stratospheric Polar Vortex is: a pool of very cold air associated with low pressure 10 to 50 km above the Winter Pole.
Around this pool of cold air we get some very strong westerly winds propagating around it – a stratospheric jet stream – high up above our own tropospheric jet stream – which helps to keep the Polar Vortex intact above the pole. Westerly winds are of course associated with the anti-clockwise movement of air in low pressure systems in the northern hemisphere.
However, the Polar Vortex can sometimes be affected by natural weather systems or disturbances in the lower part of the atmosphere which can weaken the stratospheric jet stream. This then causes the air in the stratosphere to compress leading to a rapid temperature increase. In turn the Polar Vortex breaks down or becomes displaced from the pole and we get what is referred to as a Sudden Stratospheric Warming event or SSW. SSWs are subject to categorization: Major, Minor and Final.
A major SSW event is when the observed stratospheric temperatures rise rapidly over the course of a few days and instead of a pool of cold air associated with low pressure over the pole (a polar vortex) we get an area of high pressure, associated with the rapid rise in temperature. As a result, the stratospheric westerly winds change direction to easterly which is associated with the clockwise movement of air in high pressure systems in the northern hemisphere.
Why are SSWs significant for our weather?
Normally, the air flow in the stratosphere during winter is westerly, moving around from west and east because we have low pressure at the pole. This enhances the Jet Stream lower down in the troposphere. Typically we tend to get reasonably strong Jet Streams propagating around the winter hemisphere anyway because of the surface temperature difference from equator to pole during winter. But when the Polar Vortex is present in the Stratosphere it helps to strengthen the Jet Stream, which is what drives low pressure systems and winter storms from the Atlantic towards our area.
When the Polar Vortex breaks down or gets displaced from the pole, that helping hand is no longer there and so the Jet Stream lower down in the troposphere can and does weaken. The tropospheric jet also gets pushed further south leading to the development of high pressure systems at higher latitudes. The easterly winds in the stratosphere effectively sink down into the troposphere, altering the weather patterns in the northern hemisphere.
It’s important to note that an SSW doesn’t necessarily mean we’re going to get continuous cold weather for the rest of the winter. What it does mean is that there is a greater chance of an easterly flow type set up which could bring episodes of colder weather depending on the synoptic set-up.
Has a major SSW occurred this winter?
In short yes. It peaked at the beginning of January 2019.
What will be the effects and when will we start to see them?
It takes a long time for the easterly winds to filter down into the part of the atmosphere where we live – generally a number weeks at least. The Sudden Stratospheric Warming (SSW) event which occurred at the start of January is expected to impact tropospheric conditions towards the end of January. If the resulting high pressure systems become established over Scandinavia or Greenland, such a synoptic pattern could lead to bitterly cold air from eastern Europe/Russia pushing in over Ireland, as happened in late February/March of last year (2018). It is important to note that this kind-of set-up can just be the result of normal weather variability, but the main point is that a major SSW can enhance the likelihood of occurrence.
At the moment, our weather is expected to be either milder than or near average out to the next 7 to 10 days, with an Atlantic regime gradually returning as high pressure slips away to the southwest. With the exception of mountaintops, snow is therefore unlikely over the next 7 to 10 day period. As we approach the end of January, though, the guidance suggests an increased risk of colder than average weather with frost and ice likely to be more prevalent than of late. Whether we will get the synoptic set-up which could result in snowfall remains highly uncertain. But as always, we’ll keep you posted.
You can view the Atlantic charts 7 day forecast for rainfall and airmass here
Information to follow was included by Meteorologist Liz Walsh on Tuesday 27th November
The cool easterly airflow which persisted for much of last week has now given way to a much more unsettled but milder Atlantic regime. It’s a complex set-up out in the Atlantic at present with several low pressure centres and frontal waves in the mix. The first active period of weather from one of these low centres, which produced very wet and windy conditions for many on Tuesday morning the 27th November, has cleared and there will be a lull in the weather through the rest of Tuesday before the next system arrives.
This next low pressure system carries (and will keep) the name of Storm Diana. It was named by the Portuguese Met Service due to the orange level warning conditions it produced for the Azores archipelago on the evening and night of Monday the 26th November. Storm Diana will produce some severe and potentially damaging winds as it moves northwards to the west of Ireland on Wednesday and a number of warnings have been issued in relation to this event.
Satellite Image of Storm Diana in the Atlantic
A yellow wind warning has been issued for the 26 counties that we have responsibility for. Winds are expected to reach mean wind speeds of 55 to 65km/h and gusts of 90 to 110km/h. Additionally two orange level wind warnings have been issued for the southern and western coastal counties of Cork, Kerry, Waterford, Wexford, Clare and Galway to warn of the potential for orange level winds – mean speeds of 65 to 80km/h and gusts of 110 to 130km/h. These orange level winds will mostly occur in coastal regions of these counties and about high ground and there is also the added risk of coastal flooding due to very high seas.
The strongest winds on Wednesday will be coming from a slightly different direction (south to southwesterly) than the strongest winds on Tuesday (southeasterly), which will produce some differences in how they are experienced in different parts of the country i.e. weaker or stronger depending on exposure.
Accompanying the wind, some heavy rainfall as well, with Connacht and west Ulster likely to bear the brunt of the wettest conditions.
Information to follow was included by Meteorologist Liz Walsh on Thursday 8th November
Yellow weather alerts have now been issued by the forecast office for Friday 9th November.
The area of low pressure we have been watching is now about 1200km east northeast of Newfoundland in the Atlantic (circled in red on the satellite image below). It will soon begin to deepen rapidly over the next 24 hours as it swings eastwards across the Atlantic before it makes a turn northwards on Friday morning around 500km off the west coast of Ireland. Rain and wind associated with this vigorous system will begin to affect the west and southwest of the country between 4 and 6am on Friday.
The rainfall warning covers a number of counties including Mayo, Galway, Cork, Kerry, Tipperary, Waterford, Wexford, Wicklow, Kilkenny, Kildare, Carlow, Dublin and Louth and is valid from 6am to 6pm. Rain will become widespread on Friday with some intense bursts of rain occurring over a relatively short time period which will lead to spot flooding. The heaviest of the rain will occur in the west and southwest during the morning and early afternoon. The focus of the heaviest rain will then transfer eastwards through the early and late afternoon, with the rain giving way to scattered showers in the west and southwest.
The wind warning has been split to accommodate the timing of the strongest winds in different parts of the country. The Connacht and Munster wind warning is valid from 4am to 3pm, while the Leinster and Ulster wind warning is valid from 8am to 7pm.
As the wind is coming from a rapidly deepened low, the atmosphere will be unstable which means that gusts will feature prominently in many areas. Most of the gusts will be within the limits of our yellow warning criteria – up to 110km/hr – but exposed coastal regions and areas of higher ground inland, especially in the southwest, south and southeast, will experience gusts greater than this – possibly up to 125km/hr. Winds of this speed can cause significant damage and caution is advised.
There is also a risk of coastal damage, especially on parts of the east coast as winds, high spring tides and storm surge combine to produce spray and wave overtopping.
Information to follow was included by Meteorologist Liz Walsh on Wednesday 7th November
It’s been a rather unsettled week of weather so far with spells of wet and windy weather. Excess water has occurred on the roads at times, with spot flooding compounded by autumn leaves blocking drains.
Our weather will remain unsettled through the rest of this week, and Met Éireann forecasters have been monitoring developments for this Friday 9th November particularly closely. There are a number of low pressure systems or depressions dotted around the North Atlantic at present, but the one we are particularly interested in is an area of low pressure over Newfoundland in Canada which is expected to move out into the Labrador Sea tonight, Wednesday night.
This low pressure system will travel eastwards across the Atlantic by Friday, helped by a strong jet stream which will serve to deepen the low significantly by the time it comes close to our shores. The (by then) deep low will travel northwards to the west of Ireland during Friday, and the associated fronts will track in over Ireland during Friday morning and afternoon bringing strong winds and heavy rain and there is potential for severe and damaging gusts, especially on coasts. There is also a risk of coastal damage due to wave overtopping, with the timing of the strongest winds coinciding with high tide on some coasts.
We’ll be closely monitoring forecast data from our 54-hour high resolution model, HARMONIE over the next 12 to 24 hours with further updates to follow.
See the first hourly wind and rain projections for Friday morning 9th Nov from HARMONIE below:
Information to follow was included by Meteorologist Liz Walsh on Tuesday 30th October
The National Hurricane Center continues to issue advisories for Hurricane Oscar in the western subtropical Atlantic. The system is expected to become a post tropical storm on Wednesday night as it continues to track north-northeastwards. The current track guidance has Storm Oscar tracking between Scotland and Iceland during Saturday.
What is the significance of this to Ireland?
A cooler than average regime has persisted over Ireland since the beginning of the bank holiday weekend. The atmospheric pattern has been, and will continue to be, generally slow-moving and meridional over the next couple of days, dragging cold air down from the north and northwest, while the Atlantic westerly flow we are used to is essentially blocked off. The main significance linked to the passage of Oscar to the northwest of our shores, is that we will see a return to a more mobile Atlantic regime with frontal passages and/or low pressure systems bringing spells of rain and strong winds at times, as well as fluctuations in temperature.
When will Oscar affect us and what will be the effects?
At present, it looks as through frontal zones associated with post tropical storm Oscar will start to push in over Ireland on Friday. Moist tropical maritime air will be transported northeastwards over the country during Friday and temperatures on Friday evening look likely to be up around 12 to 14 degrees Celsius – this despite widespread rain with some heavy falls, and blustery southerly winds. Current indications suggest that the strongest winds associated with post tropical Storm Oscar will likely be in coastal regions of the west and northwest during Saturday, with gales or potentially strong gales in those sea areas.
Current forecast pressure and airmass temperature from our website for midnight on Friday night into Saturday morning.
As is often the case in weather forecasting, and especially with respect to transitioning tropical systems, there will continue to be a level of uncertainty in the evolution of events, so do stay up to date with the latest forecasts. Warnings and advisories will be issued closer to the time, if and as required.
Information to follow was included by Meteorologist Siobhán Ryan on Tuesday 16th October.
One year on from Ophelia, and what an exceptional 12 months it has proved to be.
One year to the day – Blackrock Park, taken this morning October 16th 2018, by Gerry Lumsden
Following on from Ophelia, the only other wind storm to occur last autumn was that of Storm Brian, which affected the country to a lesser extent on Saturday 21st October.
The winter season was an average one overall, with the usual unsettled spells, which the dark winter months normally deliver. Further stormy episodes followed, especially during January, and overall it was colder than normal. Later in February the jet stream was pushed northwards as a result of stratospheric warming, causing a blocking high to anchor firmly in place, and drawing in the beginnings of the icy cold spell which overlapped into early springtime.
The spring of 2018 was characterised by a cold snowy start, but with conditions improving through the season, as it closed on a dry, warm and settled note. The first week of March was its defining period, when bitterly cold Polar Continental air moved in from the east, and Storm Emma (pre-named by the Portuguese) later moved up from the Bay of Biscay. Record breaking snow fell, but with a relatively quick thaw following the main even on the 3rd of March, the country returned back to normal after the weekend.
The summer of 2018 will be long remembered for heatwave and drought conditions, with intense thunderstorms also a feature of the early season. Large blocking highs were dominant, especially from the 21st of June to the 14th of July, which gave rise to well above average temperatures with rainfall well below average generally too. Temperatures peaked late June with the highest air temperature recorded on the 28th of the month at Shannon Airport, Co. Clare when the mercury reached 32.0 degrees Celsius. Coincidentally that same day Malin Head, Co Donegal recorded the highest daily sunshine hours of the summer, with 16.5 hours in total. As well as being warm and sunny it was also extremely dry, especially across the midlands south and east. Phoenix Park recorded the lowest seasonal rainfall total, with just 75.3mm of rainfall, which equates to 38% of the LTA. It comes as no surprise that this was also its driest summer since 1995.
The 2018/2019 wind storm season has got off to an early start with three named storms to date; Storm Callum of course the most recent one. The other two storms occurred during September and were named Ali (19th) and Bronagh (20th). The highest September 2018 wind speed was a gust of 146 km/h at station Mace Head, County Galway on Wednesday 19th at 08:11 UTC during Storm Ali.
In the previous storm season, there were 11 named storms, beginning with Aileen (12th September 2017) and ending with Hector (13th June 2018). Storm Ophelia (2nd storm of the season, after retaining its name under protocols with the National Hurricane Centre in Miami), was of course the most memorable and serious one, with a record gust wind speed of 156 km/h observed at station Roche’s Point, County Cork on Monday 16th October 2017 at 10:59 UTC.
Today of course couldn’t be any more different to this day last year, with the skies continuing to brighten up this afternoon as autumn sunshine across Atlantic counties extends eastwards. Though it has been a small bit breezy, with a small craft warning still in play, the winds will gradually ease down too.
Information to follow was included by Siobhán Ryan and Dr Sandra Spillane on Monday 15th October 2018.
The remnants of Hurricane Leslie have wreaked havoc, mixing with the lower levels of the atmosphere across the eastern Mediterranean. A triple point (where the occluded front, cold front and warm front all intersect) moved into this southern area, resulting in enhanced lifting and significant wind shear. Severe weather can sometimes occur at this intersection point. Case in point, most tragically in this situation, especially given the origins of the airmass, with the local topography (high mountains and rushing rivers) another contributing factor.
The highest RED level warning, issued by by Météo France, remains in operation in the south of the country. Torrential rain and catastrophic flash flooding have majorly impacted upon the area of Carcassonne, with up to 4 months rain falling in just a few hours. Floods like this (especially around the Aude river) have not been witnessed since the year 1891, with as much as 100 to 250 mm of rainfall recorded in a 4 to 6 hour window. In Trébes the floodwater was reported to be as high as 7 metres. The death toll has been revised down from 13 to 10.
In Ireland, daily rainfall totals above 150 mm have occurred between August and December, in 9 years since 1941 of which 3 occurrences have been since 2000. Climate models have projected a notable increase in the frequency of ‘very wet days’ (>30mm) over most of the country for the autumn and winter months (Nolan et al, 2015).
The highest daily rainfall total, since 1942 in Ireland, was 243.5 mm of rainfall measured at station Cloone Lake (Caragh River Area), County Kerry on Saturday 18 September 1993, representing 209% of its monthly Long Term Average (LTA) and has a rainfall return period of 156 years (occurring any month). The highest during October was also observed in County Kerry with 201.2 mm at station Waterville on Monday 3 October 2016, representing 140% of its monthly LTA.
Nolan, P, et al. 2015. Ensemble of regional climate model projections for Ireland. Environmental Protection Agency.
The Met Éireann Forecaster’s Commentary page provides the public with a supplementary severe weather discussion. Posts will only be added when required and will be archived at the end of the page when the event is over, so the details can still be viewed.
Information to follow was updated Friday 12th October by Meteorologists Siobhán Ryan and Dr Sandra Spillane, with contributions from Dr Emily Gleeson and Liz Walsh.
Met Éireann named Storm Callum on Wednesday 10th October. Severe Orange and Yellow Wind Warnings were issued, valid for Thursday night and Friday day.
Note: The Severe Orange Warning extends to 16:00 for Donegal, Sligo, Mayo and Galway, with warnings having lapsed now elsewhere.
South to southwest gale to storm force winds remain in effect for all Irish sea areas, with the risk of violent storm force winds no longer a concern. Those gales will continue Friday evening on coasts from Slyne Head to Malin Head, as well as on the Irish Sea, whilst moderating at sea elsewhere. Swell conditions are forecast well into Friday night, even though the winds will ease off for all sea areas.
Further warnings were considered across parts of the south and east later Friday, owing to another swathe of wind and rain. However the severity and likelihood of this secondary event diminished considerably from run to run.
This event was always predominantly a coastal one, though some severe gusts moved inland, especially close to the squally thundery cold front, as it pushed up over the country overnight. Gusts in excess of 90 km/h were recorded widely, with up to 125 km/h gusts in parts of the west. The severe ORANGE warning still in operation for west and northwest coastal counties will shortly lapse, with the strongest gusts along exposed coasts here.
Meteorological Situation 13:00, Storm Callum, with central pressure 947hPa, is now centred 150 Nm northwest of Belmullet. It continues to track northwards towards Iceland and fill, with the south to southwest airflow slowly moderating as it enters a more mature stage. With a tight squeeze on the isobaric gradient however, some very strong winds are still expected in the west and northwest into that late afternoon, along with ORANGE level gusts here. The trailing waving cold front has been moving back up from the south early this morning. That heavy swipe of rain will continue to affect much of Munster, Leinster into the afternoon, with other parts of the country seeing some falls of rain, as it tracks northeastwards. Parts of west Connacht and west Ulster may escape dry though, as it clears into the Irish Sea before early evening. A much drier, calmer and comparitively brighter picture later so, but misty conditions locally where rain has presented today.
Importantly, even though the winds at sea will die down later Friday, there is concern for very high sea swell well into the night-time hours
A complicated set-up as the effects of the same waving front pulsate back up across Ireland tonight and into Saturday. A cut off low will push up over the country too, with slow moving weather fronts wrapped around its centre. Exact details may prove tricky, but suffice to say it will be a very wet day across most of the country. Rainfall totals may approach 24 hour warning levels in parts, but of course this will be monitored and if need be relevant warnings will be issued. The strong warm conveyor belt has the potential to feed up some locally high totals.
The transient ridge of high pressure still appears to move in on Sunday with a quiescent day in store for all. The remnants of Hurricane Michael will pass well to the south of Ireland, moving towards the northwest of Iberia by early nightfall on Sunday.
Meteorologist Liz Walsh of Met Éireann talks about the very latest weather associated with Storm Callum, 12:00 Friday 12th October.
- Highest gust so far 67 Kts Belmullet 7am Friday 12th October
- Moore Park County Cork recorded 20.6mm rainfall in just a 4 hour window overnight, with 30mm by 14:00 Friday.
- Some high totals recorded in a one hour window along the squall line last night too.
- Some significant lightning was also reported by night.
- 17.1 m individual wave height recorded at Buoy M3, off the southwest coast.
- Staggering and record breaking drop in pressure during a 24 hour window – close to 48mb.
The first image below shows the passage of last night’s cold front and squall line (the line of rain along the spine of the country brought some intense bursts of rain with thunderstorm activity reported, as highlighted by the coloured cross symbols on the chart below). The second image below shows the radar Friday daytime.
The following images are HARMONIE forecast wind and pressure patterns for 06:00, 12:00, 15:00 and 18:00 on Friday (06:00 run).
Video below was recorded on Thursday afternoon 11th October in GFD, Met Éireann HQ.
The following is the ECMWF forecast wind and pressure pattern for early Saturday night.
Meteorological Situation 06:00 Thursday 11th October, Storm Callum is the 3rd named storm of the 2018/19 season. Not yet formed, but later Thursday into early Friday, a rapidly deepening Atlantic storm depression (936hPa), will advance towards the west of Ireland and track northwards, eventually pulling away towards Iceland daytime Friday.
Main concerns – the strongest winds associated with this event will occur during the night-time hours and Friday morning rush-hour commute. Even though the high winds will be the main concern, a spell of heavy squally rain will occur too overnight too, making for an extremely windy and wet one, as the associated cold front quickly tracks north-eastwards across the country. Possibly damaging southeast winds will veer southwest after the passage of this front, with the strongest of the winds set to impact coastal areas. Additionally there is a concern for storm surge, coastal flooding, and overtopping of waves around Atlantic coasts, due to the coinciding high spring tides. Very high seas are expected too, along with strong gale to storm force winds at sea. With trees still in part leaf, there is a concern for felling as well. Members of the public should bring in wheelie bins, any garden furniture etc. before the start of the event.
Though the winds will begin to ease down by midday for all but west and northwest coasts; a sting in the tail may yet follow, with a deterioration possible later Friday, as the trailing waving weather front potentially feeds pulses of rain from the south, with the possibility of a further core of strong southerlies too. However the likelihood and severity of this secondary event seems to be diminishing considerably from run to run.
#StormCallum #stoirm #storm https://www.winterready.ie/en
ORANGE WARNING – Be Prepared
An ORANGE level warning is issued by Met Éireann for wind speeds with the capacity to produce dangerous, stormy conditions which may constitute a risk to life and property.
- Stay away from exposed coastal areas for the period of the ORANGE warning.
- Drive to anticipate strong cross winds and other hazards such as falling/fallen trees. High sided vehicles and motorcyclists are particularly vulnerable to strong winds – slow down and give extra space to pedestrians and cyclists.
- Be aware of local conditions in your area; wind strengths can vary significantly from place to place (depending on direction and local topography).
The other two storms occurred during September and were named Ali (19th) and Bronagh (20th). The highest September 2018 wind speed was a gust of 146 km/h at station Mace Head, County Galway on Wednesday 19th at 08:11 UTC during Storm Ali. Generally, the winds were south-westerly overall during the month. In the previous 2017/2018 season, there were 11 named storms, beginning with Aileen (12th September 2017) and ending with Hector (13th June 2018). This season was notable for Storm Ophelia (2nd storm of the season, after retaining its name under protocols with the National Hurricane Centre in Miami), with a record gust wind speed of 156 km/h observed at station Roche’s Point, County Cork on Monday 16th October 2017 at 10:59 UTC. In the past 30 years, there has been an average of 6 days per year where storm force winds have been observed at a national wind station.
Wind speed records since 1942 (any month)
- Mean: 131 km/h (Hurricane Force) Foyne’s Airport, County Limerick 18th January 1945
- Gust: 182 km/h Foyne’s Airport, County Limerick 18th January 1945
Wind speed records during October
- Mean: (Violent Storm) 115 km/h Roche’s Point, County Cork 16th October 2017 Ophelia
- Gust: 178 km/ Rosslare, County Wexford 24th October 1995
An average warming of 1.5°C across the whole globe raises the risk of heatwaves and heavy rainfall events, amongst many other potential impacts. For Ireland, climate models also project a decrease in the overall number of storms, however an increase in extreme storm activity by mid-century is projected (Nolan et al, 2015).
Nolan, P, et al. 2015. Ensemble of regional climate model projections for Ireland. Environmental Protection Agency.