JULY 2021 MUCH DRIER, WARMER AND SUNNIER THAN
Armagh Observatory reports that July was the driest at Armagh for 21 years, the warmest for eight years and the sunniest for three years.
Total precipitation was 25.55 mm (1.01 inches) including three trace values (i.e., 25.4 mm if trace values are ignored). This was approximately 35% of the 183-year long-term (1838–2020) average precipitation at Armagh (73.4 mm) and 37% of the most recent (1991–2020) 30-year July average (69.0 mm), making this July the driest at Armagh since July 2000 (13.3 mm), and the thirteenth-driest July at Armagh on record.
The wettest day was the 4th with 15.9 mm (0.6 inches) of precipitation, mostly associated with a heavy thundery shower around lunchtime that day. The second-wettest day was the 27th with 5.2 mm of rainfall. Thunder was noted on the 4th and during late afternoon on the 12th. A rare, spoked rainbow was observed near Clogher on the evening of the twelfth.
The mean temperature (the monthly average of the daily maximum and minimum temperatures) was nearly 17.9 degrees Celsius (64.2 Fahrenheit). This was approximately 3.0 C warmer than the 225-year long-term (1796 2020) average July temperature at Armagh (14.87 C) and nearly 2.2 C warmer than the most recent (1991–2020) 30-year July average (15.72 C). This was the warmest July at Armagh for eight years, that is, since July 2013 (mean temperature 18.2 C), and the fifth-warmest July at Armagh since daily temperature records began at the Observatory around 1796. The five warmest Julys at Armagh are now 1989 and 2013 (both 18.2 C), 1983 and 2006 (both 18.0 C) and 2021 (17.9 C).
July 2021 was remarkable for an exceptionally long spell of hot weather during the second half of the month. For each of ten days, from the 16th to 25th July, the maximum daily temperature reached or exceeded 26.0 C (78.8 F). The 21st briefly recorded a value (30.5C), which at that point was the highest ever recorded at Armagh. This record was broken the following afternoon (the 22nd) by 31.3 C, equalling that reported from Castlederg, Co. Tyrone, the previous day. The UK Meteorological Office defines a heat wave in Northern Ireland to be any period of at least three consecutive days when the maximum daily temperature meets or exceeds 25.0 C (77.0 F), so short heat waves are not uncommon. However, those lasting at least ten days are much more unusual. The last time this happened at Armagh during July was 38 years ago during a spell of hot weather lasting from the 6th to 15th July 1983.
July is usually, but not always, the warmest month of the year. Over the last 40 years, the mean July temperature at Armagh has been an average of 1.8C warmer than June and 0.4 C warmer than August. It is therefore interesting to note that in a world of increasing global average temperatures recent 30 year July average temperatures at Armagh have been slowly rising. Thirty years ago, the (1961-1990) 30-year average was 15.2 C whereas the most recent (1991-2020) 30-year average is 15.7 C. This is consistent with average summer temperatures at Armagh increasing roughly in line with global warming, currently at approximately 1.7 degrees Celsius per century.
The warmest day this month (highest maximum air temperature) was 31.3C (88.3 F) on the afternoon of the 22nd, preceded by 30.5 C on the 21st and followed by 29.2 C on the 23rd. The coldest day (lowest maximum air temperature) was 18.0 C, which occurred on three days: the 28th, 29th and 31st. The highest minimum air temperature was 15.1 C on the morning of the 22nd, and the lowest minimum air temperature was 10.0 C on the 7th. There were no nights with ground frost (grass minimum temperatures less than or equal to zero Celsius).
This July also recorded a total of 160.0 hours of strong sunshine at Armagh. This is approximately 18% more than the corresponding 140-year (1881-2020) long-term average (135.6 hours) and nearly 19% more than the most recent (1991-2020) 30-year average (134.8 hours). This was the sunniest July at Armagh for three years, that is, since 178.9 hours of strong sunshine was recorded in July 2018.
The sunniest days were the 16th and 17th, which both recorded 13.6 hours of strong sunshine, followed by the 21st with 13.1 hours. 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