“A heat-period is defined as day(s) on which a Level 3 Heat Health Alert is issued and/or day(s) when the mean Central England Temperature is greater than 20°C; between June and August 2022, there were five heat-periods that met this criterion.” Source: MET Office.
I have watched a number of Preppers YouTuber channels for some years and note that they are developing their own homegrown weather forecasting, ignoring severe heat events, and “poopooing” the accepted science of meteorology & empirical data. They believe that the above temperature of 20°C is too low, though fail to provide any indication as to why.
The problem lies in data. The failure to grasp the data, understanding mean temperature, and the fact that aggregated data produces a monthly mean which is lower than 20°C. Average temperature for the UK for June, July, August & September 1961-2020 is between 14-18°C so therefore 20°C is the anomaly & marker for a heatwave. The suggestion that ti’s is too cool fails to take humidity into account.
The climate of the UK has always been characterised as unsettled and predominantly rainy. The weather is the Englishmans favourite topic for discussion- Cold, wet & windy. Therefore this would indicate there is is a high level of airborne moisture. While the weather is cool the airborne moisture is hardly noticeable. Add some additional heat to the mean and quickly we enter the realm of the unbearable and dangerous.
The Dangers of Dismissing the Warnings
I think that Preppers would prefer a heatwave to be classed as 30°C or over. But failure to understand humidity & the increased carrying capacity of moisture in the atmosphere brought on by warmer air. It’s either a failure to understand or flat out denial of science or both.
Setting the bar higher is a mistake. It would not take into account situations like south facing gardens, other natural and man-made environments, which become heat traps. Temperatures in heat traps can be 5-7° higher than the forecast & actual air temperature. Couple higher temperatures with humidity & sun traps can become “thermal kill zones”
Learn About & Understand Wet-Bulb Temperatures & the Impacts on life.
Solidarity Prepping: Preparing For Climate Change 