What are supercell thunderstorms and what do they mean for the UK?

The end of this hot spell of weather is in sight - bringing with it the prospect of a phenomenon known as supercell thunderstorms.

The Met Office have issued a yellow thunderstorm warning but the end comes with a bit of a bit of a kick with the mention of "multiple rounds of thunderstorms", and the prospect of a major system coming from France.

It's been a slow summer across the UK, with June starting off cool (with average temperatures 2°C below average), before rallying briefly towards the end. July has been changeable weather at first with longer, dryer and warmer spells of weather towards the end and the maximum temperature so far this year occurred on the 19 July at 31.9 C.

The current hot weather is coming to an end and if you have not been enjoying the hot and humid weather, it is about to become fresher.

What are supercell thunderstorms?

It is not unusual to experience thunderstorms in the UK but it is a little unusual to hear about supercells.

Supercell thunderstorms are rare in the UK.

They are an intense type of thunderstorm. They are the least common type of thunderstorm and they are unique in that there is rotating updraft within the storm - this is called a mesocyclone.

But there's also another factor to consider - a larger storm system approaching from France.

This system - called a mesoscale convective system (MCS) - is a cluster of thunderstorms organised into a single, large, very active storm. Think lots of thunder, lightning and lots of hail - the kind that could put a dent in your car bonnet.

They normally persist for several hours and produce large areas of rainfall.

Over the next 48 hours there is a lot of potential energy in the atmosphere. This is where there is a enough heat and moisture available for a large storm, but it needs to be triggered.

So how will it be triggered? Perhaps the best way to picture it is to imagine how popcorn pops - how do you know which kernel will go first?

It's hard to predict exactly where it will start, but you know it's coming!

The weather set-up at the moment has a weather front approaching from Ireland. At the same time thunderstorms are pushing up from France and this is generating a large area of risk where intense thunderstorms could develop.

Neil Armstrong, chief meteorologist with the Met Office, said: “Slow moving, impactful thunderstorms are expected to develop on Thursday with Yellow thunderstorm warnings already in place.

"The storms are likely to produce some localised intense downpours but, at this stage, are unlikely to be particularly extreme in the context of the UK climatology.

"While it is possible that a few places could see some very localised higher impacts, these are unlikely over a wider area and are not expected to be on the scale of recent extreme events (eg Boscastle 2004, Coverack 2017, London 2021).

“Thursday's storms are likely to be the most interesting and potentially impactful of the year so far, with torrential rain, large hail and frequent lightning likely.”

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