Author: Eric Gilbert

The description of a heatwave is when the maximum daily temperature is equal to or above the Heatwave Threshold on three consecutive days. The Heatwave Threshold for Wiltshire is 27C. The thermometer reached a maximum of 32.0C on Tuesday and 29.0C at 13.25 on Wednesday. Therefore, if as predicted, the maximum today, Thursday, equals or is higher than 27C, we technically have endured a heatwave. At 08.00 the thermometer read 21.3C and was rising rapidly.

The Wednesday maximum, was 29.0, which made it the second hottest day this month being 6.3C above average. The thermometer only slowly fell overnight to a minimum of 15.1C at dawn, being 3.3C above average. Thankfully, this was 3C lower than the previous hot night.

The sunos Thursday, initially weakened by thin cloud in the eastern sky, soon rose above it and was shining strongly.

Yesterday was the eighteenth dry day this month. The rainfall total for July is now 31.4mm, which is 52% of the 35-year average, whereas the equivalent rainfall lost through evaporation from ground sources and plant life is 80mm.

Temperature at 08.00: 21.3C (70F)

Temperature at 09.00: 25.2C (77F)

Temperature at 10.00: 27.9C (82F)

Temperature at 11.00: 29.7C (85F)

Temperature at 12.00: 31.9C.(89F) – cloud building

Temperature at 13.00: 31.7C – mostly cloudy with high humidity

Temperature at 14.00: 31.2C – ribbon of cloud moving south to north obscuring sun

Temperature at 15.00: 31.5C

Temperature maximum of 32.6C (90.5F) at 16.10 making it the hottest day since 1st July 2015

The south easterly air flow brought heat from far south that pushed the thermometer to a maximum 32.0C at 17.35. That was the hottest day since 21st June 2018 and 9.3C above the average.

Although it was hot, with nearly 11 hours of sunshine, the solar energy peak was not as high as recent days. The UV level was recorded as high at 6.9, when recent days have been very high.

Just after midnight thunderstorms drifted in from the south producing 12.2mm of welcome rainfall. That brought the July total to 31.4mm, still well below the 35-year average of 59.9mm.

It was a very warm night with the minimum of 18.2C at 06.02 being 6.4C above the 35-year average.

Wednesday started sunny, once the sun had risen above cloud drifting to the east. However, just after 07.30 cloud and mist drifted in blocking out the sun.

Update on Wednesday at 14.05: the description of a heatwave is when the maximum daily temperature is equal to or above the Heatwave Threshold on three consecutive days. The Heatwave Threshold for Wiltshire is 27C. The thermometer reached a maximum of exactly 32C on Tuesday and 29.0C at 13.25 on Wednesday. Therefore, if as predicted, the maximum on Thursday equals or is higher than 27C, we technically have endured a heatwave.

Monday saw the early effect of the hot air being brought to us on a south westerly air flow from North Africa as the thermometer steadily rose ta maximum of 25.6C at 16.05, which was 2.9C above average. The humidity was high all day, around 70%, making it feel very uncomfortable, when under such heat it is around 40%.

Another dry day with the UV level at the top end of the very high category.

Overnight the thermometer dipped away to a minimum of 12.8C at 04.38, being 1C above average.

Fog formed in the early hours with visibility at 05.00 restricted to 100m.

By 08.00 the thermometer had risen to 16.6C and the fog thinned, under the influence of continuous sunshine, with visibility improving to 500m. Not surprisingly, the humidity at 08.00 was very high at 98%, the highest since 2nd February.

Update on Tuesday at 16.20: thermometer maximum of exactly 32.0C at 17.35. This was 9.3C above average and the hottest day in 2019. My weather station is on the north east boundary of Marlborough so the peak temperature in town would have been a degree or two higher.

The southwesterly breeze brought milder air with the thermometer rising to 22.3C on Sunday, just 0.3C below average. This mild, moist air continued overnight producing a very mild night with a minimum just before midnight of 15.3C, which was 3.5C above average, the warmest night since 25th June and up 5C on the previous night minimum.

Monday arrived with complete cloud cover blotting out any chance of sunshine, the thermometer having risen further to 18.3C at 08.00.

The barometric pressure has been rising over the past two days, current reading of 1021.1mb, as the ridge of high pressure intensifies with the promise of more warm/hot, dry weather.

Update on Monday at 16.20: thermometer rose to 25.6C at 16.05 making it the second warmest day in July being 2.9C above average. Humidity very high at around 70% for most of the day.

After the cloudy and wet day on Friday, Saturday saw the sun return as the barometric pressure began to rise giving us nearly 10 hours of sunshine and a much warmer day, although below average (-1.4C) with a maximum 21.3C.

It was a dry day except for a light shower mid-morning. Rainfall in July stands at 19.2mm but evaporation has risen to 70mm.

The past night was 3C cooler, and below average (-1.4C), than the previous very warm night with a minimum of 10.4C at 05.35.

After initial brightness at dawn on Sunday cloud quickly blotted out any sunshine. However, at 08.02 the cloud began to break up allowing bursts of sunshine.

Update on Sunday at 18.10: late afternoon sunshine raised temperature to a maximum of 22.3C at 17.56, just below average, with UV level rising to very high.