DECEMBER 2021 WETTER, WARMER AND DULLER THAN AVERAGE. RECORD-BREAKING 2021: WARMEST SEPTEMBER ON RECORD, WARMEST AUTUMN, AND SECOND-WARMEST CALENDAR YEAR SINCE RECORDS BEGAN AT ARMAGH AROUND 1795
Armagh Observatory reports that December 2021 was wetter, warmer, and duller than average. The month was remarkable for an unseasonably very warm period beginning near the end of the month and lasting through the New Year. This was also the wettest December at Armagh for six years, and the dullest for three years, that is, since the exceptionally dull December 2018.
Calendar year 2021 was remarkable in several respects, including an exceptionally warm spell in July contributing to an equal third-warmest summer at Armagh (16.2 C), the warmest September on record (15.5 C), the warmest autumn on record (11.9 C), and the second-warmest year (10.5 C) since records began at Armagh around 1795.
The mean daily temperature for the month was 6.7 C (44.1 F), approximately 2.1 C warmer than the 225-year long-term (1796-2020) December average at Armagh (4.6 C) and nearly 1.5 C warmer than the most recent (1991-2020) 30-year average (5.2 C).
December 2021 was remarkable for a spell of very warm weather around the end of the month. According to the UK Meteorological Office, this was caused by low pressure to the west of Ireland drawing a stream of warm Atlantic air from the south-west over much of the country. Usually, but not always, the highest temperature each day occurs in the afternoon, but on this occasion the stream of warm Atlantic air led to a sequence of maximum temperatures occurring at night.
Here, the first high maximum air temperature was 12.6 C, which was observed to occur close to 09:00 GMT around the time of the weather readings on the morning of the 29th. As this was the highest temperature recorded during the previous 24-hour period the value was attributed to the 28th.
The daily maximum temperatures then increased further, from 13.2 C during the early hours of the 30th (and so attributed to the 29th) to 13.4 C in the early hours of the 31st (and so attributed to the 30th), before reaching a record 14.5 C during the early morning of New Year’s Day and so attributed to New Year’s Eve (31st December). Subsequent maxima were 13.3 C on the afternoon of New Year’s Day (and therefore attributed to 1st January 2022) followed by 11.0 C during early afternoon of the 2nd.
Following the established meteorological convention the five warmest New Year’s Eves at Armagh are now 2021 (14.5 C), 1850 (12.6 C), 1920 (12.2C), 2011 (12.1 C), and 1916 and 1936 (both 11.8 C). Similarly, the five warmest New Year’s Days (1st January) at Armagh are now 2015 (13.5 C), 2022 (13.3 C), 1851 (13.1 C), 1991 (12.7 C), and 1860 and 1922 (both 12.6 C).
The lowest maximum temperature this month was 5.4 C, which occurred during early morning of the 20th and was therefore attributed to the 19th, followed by 5.8 C, observed close to 09:00 on the morning of the 7th and therefore attributed to the 6th.
The highest minimum daily air temperature this December was 10.6 C, observed on the evening of the 30th and therefore attributed to the 31st, followed by 9.2 C on the evening of the 29th and so attributed to the 30th. The lowest minimum air temperature was 0.9 C on the 5th, followed by 1.1 C on both the 2nd and 7th. There were only 14 ground frosts this month, that is, nights when the minimum grass temperature was less than or equal to zero Celsius, the lowest two of which were minus 5.2 C on the 5th and minus 3.9 C on the 6th, and no air frosts.
Total precipitation this December was 110.85 mm (4.36 inches) including 3 trace values, that is, 110.7 mm if trace values are ignored. This was approximately 41.7% more than the 183-year long-term (1838-2020) average December precipitation at Armagh (78.2 mm) and 36.2% more than the most recent (1991-2020) 30-year December average. This was the wettest December at Armagh for six years, that is, since 186.1 mm was recorded in December 2015.
The wettest day was the 25th with 24.5 mm (0.96 inches) of rainfall, followed by 18.1 mm on the 6th and 15.1 mm on the 7th. The latter two measurements were associated with the passage of the damaging Storm Barra. This year’s Christmas Day was very wet, the third-wettest Christmas Day on record at Armagh and only slightly drier than Christmas Day 2015 (25.0 mm). With an average temperature of 7.5 C Christmas Day 2021 was slightly warmer than the mean December air temperature at Armagh.
Gulls were seen on several days, the 13th, 14th, 17th, 20th and 22nd, with a particularly large number on the 17th circling continuously and moving slowly in a north-easterly direction. A large number of gulls were also observed flying in a north-easterly direction around midday on the 20th. The frequency with which gulls have been seen this year over Armagh suggests that a colony of gulls may have become established near the city.
Rainbows were seen on the 4th and 6th, with double rainbows on the 4th and 10th. Hail was observed on the 4th, 6th, and 7th, with sleet and snow on the 6th though no snow cover. Wind from Storm Barra reached gale force on the morning of the 7th, causing tree damage and damage to the Observatory’s sunshine tower.
The month was much duller than average, with a total of only 27.8 hours of strong sunshine, this being 73% of the 140-year long-term (1881-2020) average number of hours of strong sunshine (38.0 hours) and nearly 65% of the most recent (1991-2020) 30-year average (43.1 hours).
Calendar year 2021 was a record-breaking year though with roughly average sunshine and precipitation. It was the warmest year at Armagh for 14 years and the second-warmest calendar year since daily temperature records began at the Observatory around 1795.
The annual mean air temperature was almost 10.5 C (50.9 F), approximately 1.38 C warmer than the 225-year long-term (1796-2020) average annual temperature at Armagh (9.10 C) and 0.55 C more than the most recent (1991-2020) 30-year average (9.94 C). The five warmest calendar years at Armagh are now 2007 (10.62 C), 2021 (10.48 C), 2006 (10.45 C), 1949 (10.42 C), and 2017 (10.38 C).
Total precipitation for the year was 799.65 mm including 57 trace values, or 796.8 mm if trace values are ignored. This is approximately 98% of the 183-year long-term (1838-2020) average annual precipitation at Armagh (816.15 mm) and 96.8% of the most recent (1991-2020) 30-year average (825.3 mm).
Therefore, despite some very dry and some very wet months, rainfall – as so often happens – averaged out over the year. Indeed, there is very little evidence for precipitation either systematically increasing or decreasing in the long term at Armagh. Similarly, the total number of hours of strong sunshine at Armagh during calendar year 2021 (1284.1 hours) was very close to the 140-year (1881-2020) long-term average of 1285.2 hours and the most recent (1991-2020) 30-year average (1281.0 hours).
January 2021 was the coolest at Armagh for 11 years, and wetter and sunnier than average. February was warmer than average, but wetter than average and with about average sunshine. Combined with a relatively cool December 2020, which was slightly sunnier and wetter than average, the meteorological winter 2020/2021 was cooler than average, wetter than average and with about average sunshine.
March 2021 was warmer than average, drier and much duller than average, the dullest March at Armagh for 8 years. April was much colder than average and cooler than March. This happens on average only once every 14 years in the 225-year long-term Armagh record. April 2021 was also exceptionally dry and much sunnier than average, the third-sunniest April on record at Armagh.
May 2021 was very cool, the coldest May at Armagh for six years, though this was compensated by a warm late May bank holiday. The month was also very wet, the wettest May at Armagh for 18 years, leading to the remark that it sometimes felt as if April showers had come a month late. The month was sunnier than average, and this led to meteorological spring at Armagh being sunnier than average, though cooler and with about average rainfall.
June 2021 was warmer than average. This month was exceptionally dry, the driest June at Armagh for six years, and slightly sunnier than average.
July was much warmer than average, the warmest July at Armagh for eight years. Most noteworthy was the exceptional 10-day long heatwave extending from the 16th to the 25th, during which each day achieved a maximum temperature greater than or equal to 26.0 C. A record maximum temperature of 31.3 C was recorded on the 22nd, equalling the Met Office’s Northern Ireland record of 31.3 C observed at Castlederg the previous afternoon. The five hottest days observed at Armagh are now 2021 July 22 (31.3 C), 2021 July 21 (30.5 C), 2018 June 27 (30.4 C), 1934 July 10 (30.3 C) and 2018 June 28 (30.2 C). July was also very dry, the driest July at Armagh for 21 years and the 13th-driest July on record. The month was also sunnier than average.
This record-breaking month was followed by a warmer than average August that was slightly wetter than average and the dullest August at Armagh for 13 years. The 31st recorded one of the highest August pressures on record at Armagh, a value (reduced to mean sea level) of approximately 1035 hPa.
Taking the three summer months together, the meteorological summer was the equal third-warmest summer at Armagh since daily temperature records began around 1795. The five warmest summers at Armagh are now 1995 (16.5 C), 2006 (16.3 C), and 1983, 2021, 2018, 1826 and 2013 (all 16.2C). The meteorological summer was also much drier than average at Armagh, the driest for 8 years, and slightly duller than average.
September 2021 was also exceptional. This was the warmest September on record at Armagh (15.5 C), a result that included the third-warmest September day at Armagh with a maximum temperature of 26.2 C on the 7th. September was also wetter than average and much duller, the dullest September for 38 years and the seventh-dullest September on record at Armagh.
October was the warmest at Armagh for 15 years, sunnier than average and with about average rainfall. It was an unusually calm month with no named autumn storms.
These two months were followed by an exceptionally warm November, memorable for grass growing throughout the month and for leaves remaining on some trees right up to the end of the month. November 2021 was also very dry, the driest November at Armagh for 32 years, and duller than average.
Taking the three autumn months together, this was the warmest autumn on record at Armagh, and drier and duller than average. December 2021 continued the warm trend, being warmer, wetter, and duller than average.
Miscellaneous weather notes during 2021 included a report of silent lightning on March 26th and a rare, spoked rainbow seen from Clogher on the evening of the July 12th. During the year, a wide range of birdlife has been reported, including gulls, swallows, swifts, ravens, rooks and crows, buzzards, and kestrels, as well as a jay and fieldfares.
The annual-averaged trends of temperature, rainfall and strong sunshine recorded at Armagh are shown in the attached Figures. These show respectively the mean annual temperature from 1796 to 2021, the total annual precipitation from 1838 to 2021, and the total annual number of hours of strong sunshine from 1881 to 2021.
Such figures hide significant month-to-month variability but illustrate the characteristic year-to-year variability of the weather at Armagh. Prominent features include multi-decadal oscillations and a general rise of mean annual temperature with time, the latter contrasting with a nearly constant average level of total annual precipitation, and a recent increase in strong sunshine reversing a previous downward trend.
These data refer to observations at Armagh Observatory, which has been recording the weather at Armagh since 1795.
For further information, please contact:
Professor Mark E. Bailey
Emeritus Director of Armagh Observatory
Armagh Observatory and Planetarium