AOP
Armagh Observatory & Planetarium Armagh
18 April 2018
CREDIT: www.LiamMcArdle.com

Armagh Observatory, 3rd April 2023:  Armagh Observatory reports that March 2023 was the wettest March on record at Armagh, that is, since daily rainfall measurements began at Armagh in 1838. The month was also duller and slightly warmer than average. Total precipitation was 140.75 mm (5.54 inches) including five trace values, that is, 140.5 mm if trace values are ignored. This is more than two and a half times the 183-year long-term (1838–2020) average March precipitation at Armagh (55.7 mm) and nearly 236% of the most recent (1991–2020) 30-year average (59.7 mm).

The record-breaking total rainfall for the month was boosted by a very wet day on the 31st, which recorded 27.0 mm of precipitation. This led to the previous record (114.7 mm in March 1947) being broken by more than an inch. The half-dozen wettest Marches at Armagh are now March 2023 (140.7 mm), March 1947 (114.7 mm), March 2019 (112.0
mm), March 1893 (111.6 mm) and March 1988 (108.2 mm).

Although this March was much wetter than average, February, March, April and May are usually the driest months of the year. Even this month’s very wet March ranks only 56th amongst the wettest months at Armagh in the last 185 years, and no April appears in the top ninety.

The wettest day, namely the 31st, had 27.0 mm (1.06 inches) of rainfall. This was followed by 18.8 mm on the 16th and 17.5 mm on the 9th. The very wet 31st March is now the seventh wettest March day on record at Armagh.
Snow was reported falling on five days, first on the 8th, 9th and 10th, leading to a total accumulation of around 10 centimetres on the 10th, and then again on the 13th and 14th, lying only briefly. Rainbows were seen on the 16th, 23rd and 24th, with thunder and lightning also on the 16th. Two buzzards were seen circling low over the rookery on the
afternoon of the 28th.

It is a rule of thumb that rainfall tends to average out over a sufficiently long period of time, with no significant trend over the 185 years during which daily rainfall measurements have been taken at Armagh. This is not to say that there are no decadal oscillations or that droughts or very wet periods never occur in Northern Ireland, just that dry periods will often
be followed by wet ones and vice versa. For example, last February was the driest February at Armagh for 25 years, but it was followed by the wettest March on record. This illustrates the changeable nature of our weather, particularly in late winter and spring.

Still, there is some evidence during the last thirty or forty years that March rainfall at Armagh may have started to increase compared to the long-term average. The 1961– 1990, 1971–2000 and 1981–2010 thirty-year averages are each approximately 65 mm (with a standard error of 4–5 mm), and the most recent (1991–2020) 30-year average is
about 60 mm, which may be compared to 56 mm for the 183-year long-term (1838–2020) March average. There is stronger evidence that exceptionally wet March days are occurring more often.

Over the last 185 years there have been just 23 March days at Armagh with total precipitation greater than 20 mm, a long term average of one every 8 years. However, 7 of the 23 cases have occurred in the last 13 years, showing that the current frequency of very wet March days is much higher than in the past. This year’s wettest March day (the
31st) was the wettest March day at Armagh for 13 years, that is, since the very wet 29th and 30th March 2010 (28.4 mm and 37.5 mm respectively).

The monthly mean temperature this March was 7.01 degrees Celsius (44.8 F), approximately 1.3 C warmer than the 225-year long-term (1796–2020) March average at Armagh (5.82 C) and just 0.3 C warmer than the most recent (1991–2020) 30-year average (6.75 C). This year, the average temperature for March was less than that for February. Such a reversal of the usual pattern occurs on average at Armagh only once every 5 or 6 years.

The highest maximum air temperature was 16.4 C. This occurred on two days, the 29th and 30th, and was followed by 15.8 C on the 16th. The latter was briefly the warmest day of the year before being surpassed by 16.4 C near the end of the month. The lowest maximum air temperature, notionally the coolest day, was 3.4 C on the 9th followed by 5.8 C on the 10th and 6.1 C on the 8th.

The lowest minimum air temperature, usually the coolest night, was -5.8 C on the 8th  followed by -3.6 C on the 7th and -2.3 C on both the 10th and 27th. The highest minimum air temperature, notionally the warmest night, was 9.1 C on the 18th followed by 9.0 C on the 21st and 8.6 C on the 31st. There were 7 nights with night-time air frost, and 13 with ground frost (minimum grass temperatures less than or equal to zero Celsius) of which the three coldest were -13.3 C on the 8th, -11.4 C on the 7th and -9.8 C on the 27th.

St Patrick’s day (17th March) was warm and largely dry with just 0.1 mm of precipitation. The mean temperature, with a minimum of 8.1 C and an afternoon maximum of 13.4 C, was approximately 10.8 C. This was the warmest St Patrick’s day at Armagh for 18 years, that is, since 17th March 2005 (mean temperature 13.2 C), the warmest St Patrick’s day
on record at Armagh.

With a total of 87.8 hours of strong sunshine March 2023 was rather duller than average, with approximately 85% of both the 140-year long-term (1881–2020) March average (102.4 hours) and the most recent (1991–2020) 30-year average (103.0 hours). The sunniest day was the 27th with 9.3 hours of strong sunshine, followed by the 10th and 7th with 8.0
and 7.7 hours respectively.

These data refer to observations at Armagh Observatory, which has been recording the weather at Armagh since 1795.

FOR FURTHER INFORMATION PLEASE CONTACT: Mark Bailey at the Armagh Observatory, College Hill, Armagh, BT61 9DG.

Tel.: 028-3752-2928; mark.bailey@armagh.ac.uk; URL: http://climate.armagh.ac.uk/


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