Media forecasts, including warnings, have concentrated on particularly urban areas of England and Wales, neglecting perhaps that as we approach the peak of the holiday season, there will be many looking at the information, wondering what it means for them, perhaps on a camp site or in a B & B outside the red warning area.
The red warning area doesn’t account for the Pennines or Scotland, yet it is important to note that these areas will experience extreme conditions which do pose great danger to health. If you are out and about in say the Pennines valleys do not assume the temperature will be significantly lower than in those areas defined by the red warning.
The key feature of this particular heat wave is the 'reservoir' of warm air above the ground - above an inversion, as described in yesterday’s blog.
In these conditions, where the mountain terrain itself also warms up, there will be additional heat to transfer downslope into the valleys - the outcome being that valleys within these upland areas are as warm, sometimes warmer than low level terrain remote from the hills.
As such, the weather stations at Aviemore and Aboyne punch well above their weight in terms of the number of times they turn out to be the 'warmest place in Britain'. Although primarily this is observed in the Scottish Highlands, similar impacts would be seen in other mountain areas such as the Pennines (particularly N Pennines).
The plume of extreme warmth extends north through Monday night but on Tuesday begins to accelerate away east. This makes Highland valley and mountain top forecasting tricky as the extreme warmth may be very transient.
Taking the slowest forecasts (in terms of movement away east); upland valley temperatures as far north as the Great Glen could reach 37C. More likely 33 to 35C, and taking the fastest movement away, 32C. The amount of high level cloud, a little uncertain will also have a small impact on the temperature.
With the air (above the inversion) being even warmer further south, expect 35 to 38C Borders valleys and southward along Pennines where perhaps 40C in one or two valleys.
In terms of absolute hot spots away from hills areas, the Vale of York is still going to be in line for some of the highest values around or above 40C. Nevertheless, 40C may be briefly realised near Merseyside and the west Lancashire plain.
The main message here then is simple. Do not anticipate relief from the heat in upland valleys.
So seek shelter, perhaps under trees; there will be more breeze generally higher up, (very gusty winds Pennines morning) so upland clumps of trees could well provide best afternoon siesta conditions. The humidity will be very low, meaning you may not appear to sweat. In reality sweat will evaporate rapidly, keeping your body cool - you may not feel as thirsty as a result. Nevertheless, drink, drink, drink - your body will be losing a lot of moisture in keeping you cool.
A final note on the low humidity – it exacerbates dry ground conditions and therefore the risk of fire taking hold. As such, please take note of developing closures to access land in the Peak District at least, check local information for details.
By Wednesday, this remarkable weather event will have passed. Once all the numbers are crunched and data analysed, the role of climate change can then be fully examined. However, as changes to weather patterns continue to accelerate, we are now 'rolling a six' so frequently that we can say climate change has to be a major factor in such frequent new extremes around the globe.