Republic of Ireland 2021 Summary

One of the cooler winters of recent years but relatively unsettled. Spring was mixed with a mild, dry March followed by a cold, dry April with significant numbers of frost and a cool, wet May. Summer was one of the warmest of modern times and the warmest since 2018 with a notable heatwave during July. 

January. The month of January was dominated by a southerly tracking jet stream bringing cool and wet conditions for much of the month after a mainly dry start. Blocking high pressure in the North Atlantic during the first week of January brought winds varying from an easterly to northerly direction. Precipitation at first consisted mainly of rain showers in the east away from high ground but a weak cold front moved southward on the 7th and resulted in lying snow. This introduced a northerly flow which brought wintry showers to localised parts of the southeast Dublin and Wicklow coasts in off the Irish Sea including further lying snow, particularly in Bray (Co. Wicklow) and Greystones (Co. Wicklow) with 1 to 2 cm accumulations on sea level. Blocking high pressure collapsed over the country on the 9th and brought widespread severe frosts before turning generally milder on the 11th and unsettled with rain or showers on most days. Northwesterly winds re-introduced colder air from the North Atlantic from the 21st to the 25th with much brighter weather and frosts returning. A band of wintry precipitation crossed Ireland late on the 23rd leaving lying snow in many places. Temporary easterly winds brought further snow showers to Dublin on the 24th and produced localised significant accumulations in coastal regions stretching from Malahide (Co. Dublin) to Clontarf (Co. Dublin). Atlantic fronts invaded from the southwest from the 26th with mild conditions becoming established again for most away from the north of the country where it tended to be cooler. Outbreaks of rain was widespread and prolonged at times with any sleet and snow tending to be limited to high ground or northern areas. January was nationally wetter than average with 116% of average rainfall but it was only the wettest since 2018. Mean temperatures were below average everywhere and it was nationally the coldest January since 2011 for most. The highest temperature of the month was 13.3°C at Phoenix Park (Co. Dublin) on the 28th whilst the lowest air temperature of the month was -9.2°C at Durrow (Co. Laois) on the 9th which was the lowest January temperature in Ireland since 2010 and the lowest for any month since March 2018. Sunshine was variable but most places had a sunnier than average January and it was generally the sunniest since 2010 or 2015 including Cork Airport (Co. Cork) with 95.2 hours - its sunniest since 2010. Casement Aerodrome (Co. Dublin) had its dullest January since 2013 however with 40.8 hours of sunshine. 

February. A month of two halves with a generally cold first half followed by a very mild second half. The first half was dominated by easterly winds bringing cold air from continental Europe in the second week which brought some wintry precipitation to places but accumulations were generally limited due to a cap on convection. The lowest temperature of the month was only -4.2°C at Mount Dillon (Co. Roscommon) on the 10th and no ice days were recorded at any station. Several weather fronts from the southwest attempted to displace the cold air from the 11th to 13th strengthening the easterly flow and brought widespread falls of rain, sleet and snow. Locally in parts of Co. Mayo, snow accumulations were very significant with many roads near Westport (Co. Mayo) being impassable. However, any accumulations would melt quickly as a milder southerly flow dominated the rest of the month with low pressure to the west of Ireland giving further unsettled conditions up until final few days when it finally settled down with plenty of sunshine as pressure rose from the south. The highest temperature of the month was 15.9°C at Glasnevin (Co. Dublin) on the 23rd. It was yet another wetter than average month with 136% of the average national rainfall but nowhere was it as wet as February 2020. Despite the cool first half, mean temperatures for February were mostly above average and in some parts of the east over a degree above average. It was only the mildest February since 2019 however. Sunshine was variable but mostly above average though yet again recent Februaries such as 2018 and 2019 have been sunnier. Much of the monthly totals was courtesy of the final few days as up to that point, sunshine had widely been significantly below average. Dublin Airport (Co. Dublin) recorded 10.2 hours of sunshine on the 28th - its sunniest February day on record. Belmullet (Co. Mayo) reported storm force winds on Valentine's Day with a max gust of 68 knots (126 km/h) and a maximum 10-minute mean wind speed of 51 knots (95 km/h). Cork Airport (Co. Cork) had its highest February mean wind speed since 1997 with 14 knots (26 km/h)

March. High pressure from late February continued into early March with winds veering to a southeasterly airflow which made it become cooler. There was a mixture of dull days with low cloud and fog along with some brighter days with sunny spells. There was frost in any clear skies including -3.5°C at Dublin Airport (Co. Dublin) on the 5th. Cork Airport had its lowest March grass minimum temperature since 2001 with -9.2°C on the 7th. Weather fronts from the Atlantic brought outbreaks of rain and windier conditions through second week of March with some thundery and hail showers at times too up to the 14th. However, high pressure returned again from the 15th up to the 22nd giving mostly dry and milder conditions with good sunny spells. Pressure stayed relatively high after 22nd to south and east of Ireland but it declined to the northwest allowing fronts to bring outbreaks of rain and cloudier conditions there for the final week of March. There was also a brief cold snap on the 26th when some showers turned wintry including sleet, snow and hail. The month ended mild though with southwesterly winds resulting in a maximum temperature of 17.6°C at Mount Dillon (Co. Roscommon) on the 30th, highest since 2017. It was a mostly dry month away from the northwest with 88% of the average national rainfall for March. Most mean temperatures were above average with eastern areas having the highest positive anomalies to average for the second month in a row. Milder Marches were recorded in 2017 and 2019. Sunshine was below average in the west whilst it tended to be sunnier than average in the east but not exceptionally so with March 2020 being sunnier everywhere.

April. A highly unusual and unique month in being very dry, very cool and very sunny. April was dominated by high pressure but high pressure systems tended to centre to the west of Ireland through first half as well as the final week allowing a cold northerly flow to bring cool days and cold nights whilst high pressure tended to centre over Scandinavia through the third week allowing an easterly airflow which brought milder days but nights remained on the cold side. Mild air held on in the south for the first day of April continuing from the mild end to March with a maximum temperature of 21.2°C at Valentia Observatory (Co. Kerry) on the 1st - its highest April temperature since 2011. Whilst amounts were low, there were instances of wintry showers through the first two weeks of April which consisted of snow locally, particularly on high ground. Dublin Airport (Co. Dublin) reported 19 days of air frost through April - its most for any month since December 2010 - and was its coldest April on record since records began in 1939 with a mean temperature of 5.6°C. The same station recorded 26 days of ground frost during April. However, it must be noted that after 1995, Dublin Airport had moved to a location that is more prone to colder anomalies as compared to its old placement so these figures would have been skewed by it. The lowest air temperature of the month was -4.7°C at Dublin Airport (Co. Dublin) on the 10th and Casement Aerodrome (Co. Dublin) on the 11th - their lowest April temperatures since 2013. Rainfall was well below average for all and it was generally the driest April since 2017 or 2007 following on from another very dry April for most in 2020. Four synoptic stations had their driest April on record: Oak Park (Co. Carlow) with 14.4mm (record length 15 years), Sherkin Island (Co. Cork) with 13.5mm (record length 48 years), Gurteen (Co. Tipperary) with 13.4mm (record length 13 years) and Johnstown Castle (Co. Wexford) with 12.3mm (record length 80 years). Nationally, it was the driest April since 2017 with only 33% of average rainfall. There was plenty of sunshine throughout the month from start to finish and it was nationally the sunniest April since 2015. Valentia Observatory (Co. Kerry) had its sunniest April since 1938 with 236.4 hours and second sunniest on record. 

May. Another colder than average month but compared to April, it was much much wetter. It was nationally the wettest May since 2015 with 163% of average rainfall. Valentia Observatory (Co. Kerry) had its wettest May since 2006 with 174.0mm. There was frequent areas of low pressure that brought outbreaks of heavy rain and many showery days consisting of hail and thunder. The final week of the month, with the exception of weak fronts giving cool and wet weather on the 27th and 28th, tended to be drier and increasingly warmer as pressure rose from the south. Moore Park (Co. Cork) recorded 30.9mm of rain on the 20th - its wettest May day on record since records began in 1964. Cork Airport (Co. Cork) and Moore Park (Co. Cork) had their wettest May since 1981 whilst Oak Park (Co. Carlow) and Casement Aerodrome (Co. Dublin) had their wettest May since 1993. There was lying snow on high ground early on in May and temperatures were unusually cold with an air minimum temperature of -4.0°C at Mount Dillon (Co. Roscommon) on the 6th - its lowest for May on record and the lowest May temperature for Ireland since 1979. The same station recorded a grass minimum temperature of -9.1°C on the same day. It was nationally the coldest May since 1996 with localised synoptic stations having their coldest May on record but record lengths relatively short including Mace Head (Co. Galway), Roches Point (Co. Cork), Mount Dillon (Co. Roscommon) and Gurteen (Co. Tipperary). There was as much as 19 days of ground frost at Mount Dillon (Co. Roscommon) during May with up to 5 days of air frost at several inland stations. The highest temperature of the month was 23.1°C at Newport (Co. Mayo) on the 30th. Despite being such a wet and cool month, it was also unusually a sunnier than average May for all but nowhere was it as sunny as May 2020. Belmullet (Co. Mayo) had as much as 218.0 hours of sunshine. 

June. A notably dry month, nationally the driest June since 1995 and third driest since 1900 with only 38% of average rainfall. High pressure was in control for most of June with weak fronts from time to time from the Atlantic giving outbreaks of light rain and stubbornly cloudy conditions, particularly in the northwest. It was the driest June on record at Mullingar (Co. Westmeath) since records began in 1950 with 17.4mm whilst it was the driest June since 2018 in County Dublin with Dublin Airport recording only 12.6mm, the second very dry month this year. Five synoptic stations had dry spells between 29th May and 22nd June including Dublin Airport (Co. Dublin), Casement Aerodrome (Co. Dublin), Phoenix Park (Co. Dublin), Dunsany (Co. Meath) and Oak Park (Co. Carlow) whilst Dublin Airport and Phoenix Park also recorded absolute drought conditions between 29th May and 13th June. Most places had a warmer than average June and it was the warmest since 2018 but parts of the west were cooler. The highest temperature of the month was 25.6°C at Phoenix Park (Co. Dublin) on the 13th whilst the lowest was 1.3°C at Mount Dillon (Co. Roscommon) on the 22nd. Most stations had a sunnier than average June but not exceptionally so whilst it was generally sunnier than Junes 2019 and 2020. There was as much as 190.3 hours of sunshine at Johnstown Castle (Co. Wexford). It was very dull however at Belmullet (Co. Mayo) with only 99.1 hours which was its dullest June since 2017. 

July. Warm with well above average temperatures thanks to an exceptional heatwave mid-month which resulted in the warmest July nationally since 2013. Mean temperatures were as much as over 2°C above average at Knock Airport (Co. Mayo). The first and final weeks of July brought intense thundery rainfall at times as low pressure dominated the scene and gave way to localised flooding at times, most notably Malahide (Co. Dublin) on the 27th. However, a strong ridge of high pressure from the Azores high gained control and a hot and dry tropical continental airmass was drawn up from the southeast between the 16th and 25th resulting in exceptionally high temperatures including tropical nights. 14 synoptic stations reported heatwave conditions during this period and it was the longest July heatwave on record with 10 consecutive days breaking the previous record of 9 consecutive days in July 1934, 1983, 1989, 2013 and 2018. It was also the longest mid-summer heatwave since 1995. Durrow (Co. Laois) recorded a maximum temperature of 31.2°C on the 22nd - the highest July temperature since 2006 and highest for any month since June 2018. Mount Dillon (Co. Roscommon) recorded a maximum temperature of 30.8°C on the 21st - its highest temperature on record. Valentia Observatory (Co. Kerry) recorded its highest July temperature since 1976 with 28.3°C on the 22nd. Gurteen (Co. Tipperary) recorded its highest temperature on 19th July of 29.0°C as late as 8 p.m., indicative of just how hot the airmass was. Valentia Observatory (Co. Kerry) recorded two consecutive tropical nights on 21st and 22nd July - the first time in Ireland that tropical nights have been recorded consecutively, the first tropical nights in Ireland since August 2001 and only the second time that two tropical nights have been recorded in a single year and single calendar month with July 1983 being the other. A minimum temperature of 20.5°C at Valentia Observatory on the 22nd was the highest minimum temperature in Ireland since July 1989 and joint second highest on record. Valentia Observatory also did not fall below 20°C between 5 a.m. on 21st and 9 p.m. on 23rd July. The lowest temperature of the month was 5.1°C at Mount Dillon (Co. Roscommon) on the 1st - the highest national July absolute minimum since 2013. Nationally, July rainfall was bang on average with 100% owing to the regional variation from thunderstorms and localised downpours. It was the driest July since 2000 at Ballyhaise (Co. Cavan) but even in places that were wetter than average, July 2020 tended to be wetter. Six synoptic stations had recorded dry spells between 5th and 26th July including Malin Head (Co. Donegal) lasting 22 days, Casement Aerodrome (Co. Dublin); Phoenix Park (Co. Dublin); Claremorris (Co. Mayo); Mount Dillon (Co. Roscommon) and Mullingar (Co. Westmeath) all lasting 15 days. It was a sunnier than average July everywhere owing to the heatwave mid-month which also brought plentiful sunshine nationwide as the rest of the month was generally dull. It was the sunniest July since 2013 with as much as 218.3 hours of sunshine at Johnstown Castle (Co. Wexford). 






*Averages refer to 1981-2010.

*A dry spell is a period of 15 or more consecutive days to none of which is credited 1.0mm or more of precipitation.

*An absolute drought is a period of 15 or more consecutive days to none of which is credited 0.2mm or more of precipitation.

*A tropical night is where the night-time temperature does not fall below 20°C. 

*A heatwave is a period of 5 or more consecutive days where the maximum temperature is 25.0°C or greater.