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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

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

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

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

 

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.

 

 

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