Wednesday 13th August
We have now officially had a heatwave with three successive days that saw the thermometer rise to a maximum equal to or above 27C, the threshold for Wiltshire. In fact, the thermometer climbed steadily all day under relentless sunshine, but particularly the heat from the Continent, with a maximum of 32.8C logged at 16.46 being a significant 10.7C above average. This was the fourth heatwave of the summer. The intense heat was principally due to the the Continental air as the UV level of 5.2, at the bottom end of ‘High’, was the lowest this month whilst the peak solar of 773W/m2 was the second lowest this month, due to thin, high cloud.
The heat was very slow to dissipate during the evening, dropping to 25C at 20.52 and 23C at 21.45, with a temperature of 22C at 22.24. The thermometer eventually reached a minimum of 16.4C at 05.55 early Wednesday.
Wednesday arrived quite dull under a veil of low cloud that had formed fog in the early hours with visibility down to 500m in the River Ogg valley but perhaps 1,000m elsewhere, that slowly cleared but left misty conditions at 08.00. With no early morning sunshine there was little change in the temperature by 08.00 with the thermometer having only risen a little to 17.1C. The wind has veered from the east yesterday to southwest today, as a result we come more under the influence of the Atlantic than the dry, hot Continent.
The anticyclone continues to edge eastwards over Poland with a ‘slack’ low pressure area edging in towards the West Country. The combination has brought in overnight the very humid air that read 91.0% at 08.00. However, we are still principally under the influence of the high pressure that will continue the fine, dry and calm conditions.
The loss of equivalent rainfall, through evaporation from ground sources and plant life, reached 4.7mm on Tuesday. The loss for the month now stands at 41.6mm against the actual rainfall of 3.2mm.