Thunderstorm warning and flood risk as heat breaks

How long will the current heat last?

Many of us find ourselves amidst another burst of summer heat, with temperatures once again rising above average for the time of year – something that has been lacking so far this summer.

High pressure built across the UK during the weekend, bringing warmth and sunshine nationwide. However, it’s only really continued across England and Wales. Scotland and Northern Ireland have seen cloudier skies at times, along with cooler air and temperatures around average.

This contrast will continue in the coming days too, with heat and humidity persisting across England and Wales. Temperatures here will reach the mid to high 20s, and some places the low 30s.

By the start of the weekend, cooler, fresher air will have reached all parts of the UK, but as that transition gradually takes place from midweek, there’ll be showers and thunderstorms breaking out.

Why are thunderstorms likely?

In the UK during summer, it’s quite common for spells of hot weather to come crashing to a dramatic end with thunderstorms, and this case looks to be no different.

Heat in the atmosphere is a form of energy that can fuel weather and allow thunderstorms to happen. So far, we’ve had the heat, but lacked another key ingredient – moisture.

However, that is set to change from Wednesday onwards, as a plume of humid air extends northwards out of France, seeping over England and Wales. With this ingredient in place, combined with a few other factors, the scene will be set for heavy showers and thunderstorms to happen.

Thunderstorm warnings

Given the focus of heat and humidity across England and Wales, this is where any thunderstorms are likely to be.

The Met Office has issued two yellow warnings for thunderstorms – one valid for Wednesday across southeast England, and another for Thursday that covers much of England and Wales.

A variety of impacts are possible, ranging from torrential rain, hail and lightning to gusty winds and localised flash flooding.

Why is there so much uncertainty?

Whilst confidence is high that the areas highlighted by the yellow warnings will be most at risk from thunderstorms, not everyone in the warning areas will see them, as the precise detail is uncertain.

This is because individual thunderstorms are usually small in terms of aerial coverage – typically no more than a few square kilometres, making it very tricky to pinpoint exactly where will be hit. One location can see torrential rain, whereas another place only a short distance away can see little or nothing.

As an analogy for this, think of what happens when you heat a saucepan of water. When it reaches boiling point, you know that there will definitely be bubbles of water forming in the area of water, but predicting precisely where each bubble will form is tricky.

Stay tuned for updates

Even though we are only 24 hours away from when the first batch of thunderstorms is likely to hit, given the uncertainties mentioned above, there is still scope for details to change.

So, it’s worth keeping a close eye on the forecast, as I have no doubt that the warnings will be updated, and maybe even extended and escalated, as the situation evolves.

I’ll be watching things closely in the coming days and posting more regular updates from my X, formerly Twitter, account here, and on my Facebook page here.