Heatwave & Extreme Temperature Alert


We are on dog-sitting duty near Reading (16th July) in the middle of a heatwave. The Met Office has issued a Red (Extreme Heat) warning for this coming Monday and Tuesday (18-19th July). Today at 3 pm, it is a balmy 28 ℃ in Oxfordshire with a predicted 39 ℃ for Monday! There is a good chance the UK maximium temperature record (38.7 ℃) will be broken in the next few days

Gardenning-wise, not the best time to be away. Fortunately, we have someone staying who can do some watering but the plants in the garden, polytunnel and greenhouse will be experiencing some degree of stress back in Hereford.

The UK Met Office define a heatwave as an extended period of hot weather relative to the expected local conditions at that time of the year. For the UK, a period of 3 consecutive days when the daily maximum temperature exceeds a set threshold for that location is deemed a heatwave. Threshold temperatures are set for individual counties and vary from 25 ℃ to 28 ℃. As a result of global warming, threshold temperatures are increasing especially in the South-East of England.

The UK Met Office has set a 2022 heatwave threshold temperature for Hereford at 26 ℃ though much of the UK (Wales, Scotland, Northern Ireland, the South-West and North England) retain a heatwave threshold of 25 ℃.

The plot below shows the minimum and maximum temperatures for July (up to 16th) as measured by my Davis Weather Station back home in Hereford. Based on the Met Office's current heatwave threshold of 26 ℃, the 7th - 13th July (inclusive, 7 days) was a heatwave and a new heatwave commenced on 15th July and will likely end on the 19th (inclusive, 5 days).

My definition of a 'hot' day is a daily maximum of 25 ℃ or higher and hence, by my 'reckoning', the current heatwave started on the 6th July and will not end until the 19th July at the earliest.

A key factor in being able to 'weather' heatwaves is the night time temperature - anything above 18 ℃ is likely to be uncomfortable. The chart below shows the high and low internal temperatures measured using the Davis WeatherLink Live internal module. Min/Max temperature variation is much smaller indoors than outdoors. The main point, however, is that internal temperatures have not dropped below 20 ℃ during the whole of July. A comfortable night's sleep indoors has only been possible through the use of fans.


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