Climate Statement for Winter 2020-21
Cool and wet overall, mild finish
A weakened and disrupted stratospheric polar vortex through December, January and the first half of February allowed high pressure systems to develop in polar regions, which kept the North Atlantic Jetstream displaced to the south for the majority of winter, leading to cooler than average temperatures in Ireland. The re-strengthening of the stratospheric polar vortex for the second half of February led to the Jetstream moving north again and milder conditions returning. Troughs of low pressure repeatedly stalled over Ireland during December bringing widespread rain or showers for much of the month. A short dry period around Christ-mas was followed by Storm Bella on the 26th and 27th. The first third of January saw blocking high pressure keeping it mostly dry and cool with some wintry precipitation in places. The second third saw a more active Atlantic dominated spell with rain or showers on most days and storm Christoph affecting Ireland between the 18th and 20th. The final third saw a battleground scenario over Ireland with a cold block to the northeast and milder air to the southwest pushing weather fronts in over the country, giving heavy rain in places, and some wintry falls in the North. The first half of February was cool with slow moving low pres-sure for the first week giving way to cold easterlies for the second, with further wintry precipitation in places. The second half of February was mild with low pressure to the west sending active weather fronts over Ireland from the south with some flooding in places. The month finished sunny and settled with high-pressure building from the south.
Rainfall: Above average everywhere, highest in the South and East
All rainfall totals were above their Long-Term Average (LTA) for the season. Percentage of seasonal rainfall values ranged from 105% (seasonal rainfall total of 374.8 mm) at Finner, Co Donegal to 151% (seasonal rainfall total of 416.0 mm) at Roche’s Point, Co Cork. Seasonal rainfall totals ranged from 243.4 mm (129% of its LTA) at Casement Aerodrome, Co Dublin to 625.1 mm (percentage of LTA 135%) at Valentia Observatory, Co Kerry. The highest daily rainfall total was 41.4 mm at Newport, Co Mayo on Tuesday 19th Jan. The number of rain days ranged from 60 days at Oak Park, Co Carlow to 82 days at Belmullet, Co Mayo. The number of wet days1 ranged from 43 days at Dublin Airport, Co Dublin to 71 days at Valentia Observatory, Co Kerry. The number of very wet days3 ranged from 6 days at Mullingar, Co Westmeath to 24 days at both Valentia Observatory, Co Kerry and Cork Airport, Co Cork. It was the wettest winter for the last five years at 10 stations including Phoenix Park, Co Dublin, Oak Park, Co Carlow, Dublin Airport, Co Dublin, Moore Park, Co Cork, Sherkin Island Co Cork, Roches Point, Co Cork, Dunsany, Co Meath, Johnstown Castle, Co Wexford, Valentia Observatory, Co Kerry and Cork Airport, Co Cork.
Temperature: Below average nearly everywhere
Nearly all mean air temperatures were below their Long-Term Average (LTA) for the season. Deviations from mean air temperature for the season ranged from -0.8 °C (4.7 °C mean temperature) at Markree, Co Sligo to 0.1 °C (5.3 °C mean temperature) at Phoenix Park, Co Dublin. Mean temperatures for the season ranged from 4.2 °C (at its LTA) at Knock Airport, Co Mayo to 7.3 °C (0.4 °C below its LTA) at Sherkin Island, Co Cork (its coldest winter since 2011). The season’s highest temperature was reported at Phoenix Park, Co Dublin on Tuesday 23rd Feb with a temperature of 14.6 °C. The season’s lowest air minimum was -8.2 °C reported at both Mullingar, Co Westmeath and Dunsany, Co Meath on Saturday 9th Jan (both their lowest winter minimum since 2011) while the lowest grass minimum was -12.9 °C reported at Oak Park, Co Carlow also on Saturday 9th Jan. All stations reported air and ground frost during the season. The number of days with ground frost ranged from 21 days at Malin Head, Co Donegal to 56 days at Markree, Co Sligo. The number of days with air frost ranged from 5 days at Sherkin Island, Co Cork to 33 days at Mount Dillon, Co Roscommon.
Sunshine: Above average everywhere, highest in the South
All available sunshine totals were above their Long-Term Average (LTA) for the season. Percentage of seasonal sunshine values ranged from 102% (seasonal sunshine total of 175.8 hours) at Casement Aerodrome, Co Dublin to 133% (the season’s highest seasonal sunshine total of 238.6 hours) at Cork Airport, Co Cork (its sunniest winter since 2011). Seasonal sunshine totals were lowest at Malin Head, Co Donegal with 147.4 hours (No LTA comparison*). The highest number of daily sunshine hours recorded this season was 10.2 hours at Dublin Airport, Co Dublin on Sunday 28th Feb (its highest daily sunshine for winter on record (record length 79 years)). The number of dull days ranged from 2 days at Knock Airport, Co Mayo to 43 days at Casement Aerodrome, Co Dublin.
Wind: Gales, strong gales and storm force winds reported
Seasonal mean wind speeds ranged from 6.8 knots (12.6 km/h) at Ballyhaise, Co Cavan, Mullingar, Co Westmeath to 18.0 knots (33.3 km/h) at Malin Head, Co Donegal. Gales were reported on numerous days with up to strong gales reported on 10 days during the season. Storm force winds were reported on Sunday 14th Feb and Friday 4th Dec. The number of days with gales ranged from zero days at a few stations to 21 days at Malin Head, Co Donegal. The number of days with up to strong gales ranged from zero days at Dublin Airport, Co Dublin to 5 days at both Mace Head, Co Galway and Malin Head, Co Donegal. The season’s highest 10-minute mean wind speed was reported at both Malin Head, Co Donegal and Belmullet, Co Mayo on Friday 4th Dec and Sunday 14th Feb respectively with 51 knots (94 km/h). The highest gust was 68 knots (125 km/h) reported at Belmullet, Co Mayo on Sunday 14th Feb. Only one of the three named storms during the season, Storm Bella on the 26th of Dec, brought strong winds to Ireland.
The full report is available here