Low pressure dominates

A depression is crossing the country today, Tuesday, with more lining up for the coming days as they arrive having developed over the Atlantic. The result is a succession of weather fronts that produce depressed temperatures from a regime of sunshine and showers, as on Monday.

The current barometric pressure, with a reading of 1007.7mb, is the lowest since 18th May.

The maximum yesterday was 19.3C, which was almost 1C below the 35-year average with occasional very light showers that only amounted to 0.3mm.

Overnight the thermometer fell away to a minimum of 9.1C in the early hours at 01.02, also almost 1C below average.

Tuesday saw a bright start, no sunshine, with spots of rain at 08.00 at which time the thermometer had recovered to 11.8C.

Weather report for May and Spring 2019
It was a cool May with the mean temperature just below average. The statistics show that although the daytime temperatures were in fact above average they were offset by the many cold nights that meant the mean minimum was 1.1C below average. There was only one air frost, -1.2C on the 5th, but several nights gave a ground frost with no evidence above ground, especially during the early days of May.

Warm air brought to us on a south-westerly air flow from Iberia meant a warmer end to the month with the warmest night on the 31st with a minimum of 13.9C, which was 6.8C above the 35-year average.

Although the last month of Spring was below average, the season was warmer than normal (+0.8C) with a mean of 9.71C. It is interesting to analyse the data since my station began recording in 1984 and find that Spring of that year was exceptionally cold with a mean of 6.83C. Investigating the statistics for that year I found that March was 2.1C below average, April 1.1C lower than average and May a significant 2.2C below the current average. By contrast, the Spring of 2011 produced a mean of 10.51C, the warmest from my records.

For that particularly cold Spring of 1984, hard frosts occurred on the 2nd and 4th of April with the thermometer falling to -6.0 and -5.0C. This followed a cold March that produced 11 air frosts, the coldest of which was -3.5C on the 29th.

Contrasting 1984 with the warmest Spring in 2011, although a hard air frost measuring -6.3C was recorded on 8th March 2011, no air frost occurred after 26th March or for the whole of April and May.

Although the examples above cover the past 35 years, the graph for this period shows an almost continuous rise in the mean temperature with the exception of the cold Springs in 1996 and 2013.

Rainfall in May 2018 was concentrated on three days, the 7th – 9th, when over half the month’s precipitation fell and 6.2mm, 14.4mm and 14.0mm respectively was recorded. The total rainfall for the month almost equalled the average with 59.5mm when the average is 61.0mm. There were only 6 days classified as wet days when the precipitation was equal to or greater than 1mm and 21 dry days in May.

The trend of drier than average rainfall continues into 2019. The rainfall for 2018 was 62mm below the 35-year average with 783mm. The first five months of 2019 have produced a total of 301mm a deficit of 55mm compared to the 35-year average. However, set against that figure must be the loss through evaporation from ground sources and plant life, the equivalent rainfall of 237mm.

The year of 2018 was not the driest I have recorded, as that occurred in 1996 with 594mm of precipitation, whereas six years later, in the very wet year of 2002, 1146mm was recorded.