Wednesday 16th June 2021 – Thunderstorm Chances

Thunderstorms are on their way…for some areas.

As always, thundery breakdowns are a nightmare to forecast in detail. All the models still show something different at this late stage, so I’ll do my best to aggregate the projected outcomes taking into account what has developed so far.

There are several notable opportunities for thunderstorms this evening and through the night. Some areas will miss them all, a few areas may catch them all. For thunder/lightning, I suspect anywhere as far west as Swindon is in the game (ie, so are we), but the chances of some thunder/lightning, especially frequent lightning, increase as you go further east, especially Kent, Essex, perhaps London.

Torrential downpours, are roughly equally likely anywhere from as far west as Bristol, and to the east coast – and with this the chance of localised flash flooding, possibly some damaging wind gusts and a small chance of hail.

Overall I’d suggest a 40% chance of some lightning, 20% chance of a decent thunderstorm with frequent lightning, 60% chance of some torrential downpours. As I said, it may all pass us by.

The first opportunity is this evening. Thunderstorms broke out over northern France this afternoon and are travelling across the English Channel now – but are currently struggling to survive the crossing. This could still lead to some showers in the early/mid evening hours – a low chance of a heavy downpour and thunder.

As the plume of hot air destabilises, thunderstorms over the English Channel should then find it easier to cross the channel, and also initiate over the channel – and then push north veering north-east for late evening, say 10/11pm onwards. These may form a more notable single thunderstorm system (known as an MCS), though if it does then that would increase the chance of London/south-east getting all the action from this. These storms/storm will be more likely to have lightning, torrential downpours, etc.

Overnight, scattered downpours and perhaps lightning may still occur, and then there is likely to be another batch of torrential downpours, with possible frequent lightning from elevated storms from around 4am – give or take.

It’s a really complex picture tonight and one only possible to forecast an hour or two ahead, at best. This is my best understanding of the potential – it is a dynamic situation so it could easily turn out very differently.

In summary, there is a fair chance of some lightning, a small chance of frequent lightning from a notable thunderstorm, a good chance of some torrential downpours. Some places will totally miss everything.

Don’t forget the radar and lightning detectors are available.

Full forecast tomorrow evening as usual.

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