Summer Weather Forecast 2021

Welcome to my Summer Weather Forecast for 2021.

I think if this forecast is more right than wrong, most of you should be pleased. Of course, I don’t always get it right – seasonal forecasts are experimental – at best some of the details will be wrong, at worst a month or so could be completely opposite to what I expect – competing drivers of the weather over the UK do make long-term predictions difficult.

This happened to my spring forecast – I got March and April reasonably close (though didn’t expect the amount of cold nights we had), but May I forecasted warm and sunny for most of it. Well it was for the last 5 days – does that count?! Of course not – my spring forecast was a disaster for May, though I did also suggest that that June would be sunnier and warmer than average – so far so good on that count.

So don’t take it as gospel.

Also I do ask if you can share the forecast in some way. Invite friends on Facebook, retweet on Twitter, e-mail it to your boss. Whatever works.

And a final piece of admin is to say thank you to Kira for the photograph adorning the forecast and the cover of the Facebook page for the next 3 months. A donation has been sent to Breast Cancer Now.

Background signals

Background signals generally have less influence in summer over UK weather.

La Niña has faded and we are broadly in neutral conditions, though perhaps there might be some “atmospheric memory” which could increase the chances of cloudier, cooler conditions from the north-west at times – similar to last July, but any spells should be short.

The sudden stratospheric warming event in January led to blocking highs which brought us cold weather in January, February and, arguably, April. It is my view that this pattern can persist in summer – though at this time of year, blocking highs nearly will mean warmer (unless over Greenland) and sunnier than normal conditions. I don’t think this is accepted scientific fact though – more my belief.

Sea surface temperatures around the UK are lower than normal, which would suggest that until they warm up, land temperatures will tend to be a shade lower than otherwise would be expected – though I doubt you’ll notice it.


June started very warm and sunny, and I expect this to continue into the second week, though with scattered heavy showers on a few days too, perhaps with thunder.

High pressure should remain in control for much of the month, generally close to Scandinavia – suggestions of a short hot spell around mid-month, with a breakdown to a short cooler and unsettled spell are there – before high pressure reasserts itself with more warm/very warm and fairly sunny weather. Away from the short hot spell/breakdown, low cloud may form overnight on some nights, and take a bit of time to clear in the morning.

Suggestions of something more changeable towards the very end of the month.

Overall I expect June to be sunnier than average, warmer than average with rainfall totals below average – unless one of the thundery showers is especially potent.

Confidence around 90%.


July looks a bit more mixed, and may start cooler than normal, with some rain/showers – but also some fine, sunny days in the mix.

Signals are fairly weak after the beginning 7-10 days, but high pressure should feature over or close to the UK. Whilst some changeable conditions will be likely – I’m not expecting a long-lasting settled spell like in June, I think the main theme should still be for more very warm, sunny weather – hot at times though also some thundery downpours developing on some days.

Overall I expect July to be around average for sunshine, perhaps a tad below, slightly warmer than average and slightly wetter than average.

Confidence around 60%.


In recent years we’ve often seen the summer deteriorating by late July and through August, though this year I am more hopeful that high pressure will stage a renaissance.

For much of the month, high pressure should be close to the UK, meaning many more days of warm/very warm sunshine – hot at times, but also a chance of cooler days, depending on the exact positioning of high pressure.

There is a slight signal for it to shift north of the UK at times, so this will again mean some periods where it is still very warm and sunny, but heavy, thundery showers will develop.

I don’t have a particular reading over what part of August will be the hottest, but perhaps the latter half if I’m pushed.

Overall I expect August to be sunnier than normal, warmer than normal (though that does depend on high pressure positioning) and slightly below average for rainfall (though again, catch a notable downpour and locally you may end up above average).

Confidence around 70%.

Summary and Autumn suggestions

Not bad, huh? If it comes true, of course, as I will get some things wrong – signals are particularly weak for July so it could easily end up wetter than I expect, I do feel more confident for August’s forecast than July’s.

Looking ahead to autumn…and winter…yes it is time to start thinking about winter forecasts.

Currently there is a slight signal for a wetter than normal September. There is a fairly strong signal for a cooler than normal second half to autumn – perhaps colder than normal might be more descriptive, but also drier than normal second half.

There are background signals suggesting that cold spells are more likely than normal this coming winter too.

Autumn/winter is, of course, a long way away and things can and will change in terms of background signals, so only take this as a guide for now.

Enjoy the summer.

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