Category: Commentary

Thanks to a brisk northeasterly breeze on Wednesday and a predominantly cloudy sky, the thermometer only rose to 20.8C. This was the coolest day since 27th July (20.6) and the first below average maximum this month (-0.3C). It was the breeziest day in August with a peak gust of 20mph.

The dry weather returned with the UV level of 5.0 just in the High category.

The past night was mild due to the blanket of cloud providing a duvet to minimise heat loss into the atmosphere as a result a minimum of 15.8C was 4.1C above the average.

Thursday arrived with no sun in evidence but low cloud draping the Marlborough Downs and Savernake Forest limiting visibility to 400m initially, that by 08.00 had thinned a little.

It is interesting to analyse the diurnal range of temperatures this month with which the human frame has had to adjust, day by day. The temperature variation between day and night on the 10th was 21.2C (30.6C and 9.4C) whereas by contrast the past 24-hours produced a very small range of just 5.0C (20.8C and 15.8C).

The mostly cloudy day meant the maximum temperature of 22.8C was only just above average and some 10C below the peaks a few days earlier. It was also the coolest day this month equaling that on the 5th. There were a couple of very brief, light showers that were not measurable, as the spots of rain disappeared quickly in the very dry air.

A large area of shower activity arrived from the south producing heavy rain that started at 16.55 and lasted until 18.15. The total rainfall amounted to 15.9mm, which was the wettest day since 16th March (16.4mm) with a peak rainfall rate equivalent to 38mm/hr.

Not surprisingly, in the more humid conditions, the daily evaporation that was running at over 4mm dropped to 1.35mm.

The overnight minimum of 16.1C gave us the warmest night since the 3rd (18.1C) being 4.4C above the average.

Wednesday dawned with total cloud cover and humidity registering 98%, the highest this month. The barometric pressure has begun to recover as the depression eases away with a pressure reading of 1011.3mb at 08.00, up 9mb over the past two days.

It is interesting to analyse the diurnal range of temperatures this month with which the human frame has had to adjust, day by day. The temperature variation between day and night on the 10th was 21.2C (30.6C and 9.4C) whereas by contrast the past 24-hours produced a very small range of just 5.0C (20.8C and 15.8C).

Monday was a much less hot day with the thermometer only reaching 26.8C due to considerable and variable cloud cover. This was the coolest day since the 6th but still 5.7C above the average. Twice a few spots, later;a;y were felt and seen but evaporated immediately.

Two considerable shower areas passed to the west over Swindon and east over Hungerford late afternoon avoiding once again the Marlborough area. However, a very narrow rain band passed over Marlborough at 04.15 producing just 0.3mm. Light rain was observed beginning to fall at 07.25.

Due to the residual heat and overnight cloud it was a warm night with a minimum of 15.1C being 3.4C above the average.

Tuesday arrived with total could cover and very light rain as mentioned above. Due to the complete change in the weather pattern, now a low pressure system close by also light rain, the humidity at 08.00 read 96%, which was the highest at that time for the month.

Update at 19.00: substantial rain from 16.55 to 18.15 amounted to 15.9mm.

The peak on Sunday of 33.2C was just below the high on Saturday (33.5C) but still 12.1C above the 38-year average.

Late afternoon, just after 18.00, the wind direction began to veer from the east, where it had been for four days, into the southeast and just before midnight into the southwest as a depression approached the UK.

We have now endured 8 days under heatwave conditions, for Wiltshire the heatwave threshold is three consecutive days with maxima equal to or above 27C.

The loss of equivalent rainfall due to evaporation from the ground and plant life continued to be in excess of 4mm. The statistics are, rainfall nil and evaporation 55mm.

It has been a very warm night with the thermometer not sinking below 14,5C. That low was 2.8C above the average and the warmest night since the 3rd (18.1C)

The start to Monday was so different to the last week or so. There was no blazing sunshine after dawn due to thick cloud on the eastern horizon. However, just after 07.30 there were glimpses of sunshine that an hour later were very muted due to increasing cloud.

The soil temperature at a depth if 5cm read 23.1c at 08.00, the highest this month due to the heat on Sunday and a very warm night.

The wind is due to veer further as the morning progresses to come from the west northwest or northwest as the depression advances. The barometric pressure of 1002.2mb is the lowest this month.

During the late afternoon on Saturday the thermometer soared to 33.5C after hovering around 33.4C for an hour. This maximum was 12.4C above the average and the hottest day since 19th July (36.7C).

The overnight minimum of 11.1C was slightly down on the previous night and 0.6C below the average.

Sunday brought the first obvious changes to our weather after numerous days with clear but skies there was thin high cloud that limited the strength of the sun initially. However, by 08.00 the thermometer had recovered to 19.7C.

The humidity at 08.00 was exceptionally low with a reading of just 64%.

The anticyclone is slowly retreating with the barometric pressure at 08.00 reading 1008.7mb, which was the lowest pressure for the entire month and a fall of 22mb since the peak on the 6th (1030.4mb).

Further evidence of a change in our weather is imminent with a forecast change in wind direction later this afternoon as the wind changes for the persistent easterly to southerly.