Warm first day of Meteorological Autumn

Thursday saw the thermometer rise to 21.6C in the afternoon after the sun had broken through. This was 2.7C above the average on the first day of Meteorological Autumn that covers the period 1st June to 31st August.

It was another dry although rain showers did pass to the west and east of Marlborough mid-afternoon.

It has been a mild night with the minimum no lower than 13.8C, which was a significant 4.5C above the early September average.

Saturday after dawn saw cloud increasing from the east with no sunshine.

August 2022 Review

The month began where July finished with maxima above the average starting on the 1st with 27.7C. However, a large anticyclone began to develop and settle over the country that brought a technical heatwave starting on the 7th. The maxima must be equal to or above the heatwave threshold on three consecutive days to be classed as a heatwave and for Wiltshire the threshold is 27C.

We were under a Heat Dome for six days with the extreme heat trapped beneath the high pressure as temperatures slowly built from the 7th. Interestingly, the minima were below average from the 4th to the 12th only 5.8C in the early hours of the 6th that gave relief overnight for sleeping. It was only the minimum of 12.C on the 13th that broke the trend.

The hottest day occurred on the 13th with a maximum of 33.5C being 12.5C above the 38-year average,

Throughout this period the pattern of continuous dry days continued with a run of 14 days until the first minimal precipitation on the 15th with 0.3mm.

During the first two weeks the loss of equivalent rainfall due to evaporation from the soil and plant life was considerable with a daily loss of over 4mm from the 5th to the 14th.

The first substantial rain for almost a month arrived on the 16th when a storm lasting over an hour produced 15.9mm of very welcome rain. In fact this was the wettest day since 16th March (16.4mm).

Due to the prolonged dry and hot weather humidity levels were exceptionally low with just 64% at 08.00 on the 14th when top 80s or 90% is normal. The lowest humidity I recorded was just 34% late afternoon on that same day.

The Atlantic air returned on the 19th with higher humidity that read 89% at 08.00 but no rain until the 22nd. Thus was also the coolest day of the month with a peak of just 19.6C some 1.5C below the average.

The heat returned on the 26th under a ridge of high pressure that produced quiet and settled weather with much sunshine and light winds, mainly from the northeast that persisted until the end of the month with further dry days.

It has been a record August for this station since it started in 1984 with the mean temperature a significant 2.4C above the 38-year average. Only two days produced a maximum that was below average whereas there were fifteen below average minima. Analyses reveals that the mean maximum was 3.8C above average whereas the mean minimum was only 1.0C above the average. The extremes were 33.6C on the 13th and an overnight low of 5.3C in the early hours of the 6th.

The other significant statistic was the minimal rainfall. The monthly total was just 18.mm, which was just 27% of the long-term average or 47.6mm below. It was not a record as there were two previous drier months with 12.3mm in 2003 and 5.3mm in 1995. By contrast the wettest August occurred in 1992 with 139.5mm.

Not only was it a very dry month but every month this year, bar February, produced below average rainfall. The rainfall for the period January to August was 279mm or just 55% of the 38-year average that equates to a difference of 235mm from the average.

The extremely dry conditions meant that much equivalent rainfall was lost through evaporation from the ground and plant life. There were ten days with a daily loss exceeding 4mm with an overall equivalent rainfall loss of 93.0mm for the month.

Summer 2022 Review
The average temperature for the three months of meteorological summer, from June 1st to August 31st, was 1.5C above the average. A graph of this data shows very clearly that after 1988 there was a steady rise in the average temperature until 2006, followed by a plateau until 2015, following which the rising trend returned.

The rainfall for the three months was 59.3mm, which was 119mm below the 38-year average. The driest summer was in 1995 with only 53.0mm of rainfall.