July was least sunny in 34 years, say Armagh Observatory

The observatory, which has been making observations since 1795, reports that it was duller, cooler and wetter than average in July this year.

Armagh Observatory also suggested wet Julys could be more frequent in the future.

A spokesperson said: “The mean temperature was 14.65 degrees Celsius (58.4 Fahrenheit), approximately 0.2 C cooler than the long-term (1796-2010) average July temperature at Armagh and nearly 1.1 C cooler than the most recent (1981-2010) 30-year July average.

“This was the coolest July at Armagh for five years, that is, since July 2015. The mean temperature was, unusually, lower than that of the previous month (June 2020) and more than two degrees lower than the previous July (July 2019), which had a mean temperature of 16.8 C.

“The warmest day (highest maximum air temperature) was 22.6 C (72.7 F) on the 16th, followed by 21.5 C on the 30th. The warmest night (highest minimum air temperature) was 15.2 C on the 17th. The coolest day (lowest maximum air temperature) was 14.2 C on the 14th, and the lowest minimum air temperature was 7.2 C on the 10th.

“There was just one night with ground frost, that is, with a minimum grass temperature less than or equal to zero C, namely -0.5 C on the night of the 18th/19th. This was one of the few nights that were clear enough to enable observations of comet C/2020 F3 NEOWISE in the north-west. There were no air frosts.”

The observatory spokesperson continued: “Total July precipitation was 85.05 mm (3.35 inches), including 5 trace values (i.e. 84.80 mm if trace values are ignored). This was approximately 15% more than the long-term (1838-2010) average July precipitation at Armagh (73.70 mm) and 36% more than the most recent (1981-2010) 30-year average (62.52 mm). This was the wettest July at Armagh for eight years, that is, since July 2012.

“The wettest day was the 22nd with 10.2 mm (0.40 inches) of rainfall, followed by the 21st with 9.5 mm. A flock of gulls was observed flying over the Observatory grounds on the morning of one of the half-dozen totally dry days of the month, namely the 28th.

“It is interesting to remark that while rainfall totals fluctuate significantly from day to day and month to month, and even from place to place, the long-term rainfall record at Armagh shows no evidence for any systematic trend in precipitation towards either significantly wetter or drier values. “Despite this, July rainfall totals at Armagh have tended, for an approximately 50-year period beginning around 1955, to be drier than the long-term average. More recent monthly data from the last fifteen years suggest that this behaviour has come to an end with reversion to the long-term mean. This suggests that relatively wet Julys may become more frequent than has recently been the case during the second half of the twentieth century.”

The spokesperson continued: “The total number of hours of strong sunshine was 81.5, just 55% of the long-term (1881-2010) average at Armagh and 60% of the most recent (1981-2010) 30-year average. This was the dullest July at Armagh for 34 years, and the fourth-dullest July at Armagh since daily sunshine records began at the Observatory in April 1880. The three cloudier Julys at Armagh are 1957 (65.0 hours of strong sunshine), 1986 (76.2 hours

and 1931 (81.1 hours). The sunniest day was the 19th, with 9.2 hours of strong sunshine.”