Spring Weather Forecast 2021

Welcome to my Spring Weather Forecast 2021.

Spring is my favourite season – especially late spring and early summer when it is often very warm but not too hot, and there are chances of thundery downpours – my favourite kind of weather day.

It is, of course, still early days for spring and still rather chilly as I write – but at least there is blossom on some trees, daffodils are starting to shine – the hope that spring brings never tires, and after arguably the most difficult winter collectively for decades, it is nice to just see the beginnings of spring.

I’m actually quite happy with my winter weather forecast – these seasonal forecasts will never be perfect but I thought I did a good job. We had more cold spells than recent winters and though we didn’t quite get something like February 2018 – the models teased that could happen, the sudden stratospheric warming event happened but just didn’t split the polar vortex which is likely why we didn’t quite have that newsworthy cold spell that we would have referred to for years to come.

So as I mentioned, these seasonal forecasts are experimental – I will not get everything right. Think of them more as a general guide, my hope is to get more right than wrong. I am not a professional meteorologist.

As always, I’d kindly ask you to share this forecast in some way – I don’t ask for anything other than a quarterly share/retweet or whatever your preferred action is.

And the final bit of administration is to say thank you to Eve for this classic Reading in spring photograph. A donation has been made to British Lung Foundation.

Background signals

I think background signals are less useful in spring than they are in winter, but those of note include La Niña which is weak and trending towards neutral – though there is some uncertainty as to whether it may strengthen once more May onwards – one would assume the trend to neutral continues, but some models have suggested La Niña could strengthen which would increase chances of rain/showers come summer.

In the more short-medium term, the MJO is suggested that it may go into phase 8/1, which would support the idea of high pressure to our north (ish) later in March.

The sudden stratospheric warming event from January will likely still have some impact – I believe that it increases the prevalence of blocking highs through spring, and there is more cold air at mid-latitudes because of the SSW that could be tapped into during early spring.

Finally, the polar vortex is strengthening which should encourage the jetstream to head further north – taking low pressure systems with it, especially as the influence of the SSW fades.

So quite a mixed and conflicting set of background signals as always, but there is a theme and that is of high pressure being close to the UK more than normal – so a drier and sunnier spring than normal is expected. Getting the position of the high pressure systems – and hence the source of the air and subsequent temperatures is the challenge.

March

March starts dry and mild. Towards the first weekend colder weather will spread down from the north – nothing especially cold but still cold enough with overnight frosts – a chance of a light wintry shower.

For the second week this will be replaced by more unsettled conditions with spells of wind and rain, and showers in between – temperatures average or a little below. I wouldn’t rule out sleet or snow either in any more notable north-westerlies.

That unsettled spell should be short-lived and high pressure should take back over for the rest of March – positioning uncertain at the moment and it will vary a bit. When it is closer to the UK, it will be rather pleasant, mild and sunny – when further west it will be cooler, perhaps colder with showers – a 2-3 day northerly plunge with wintry showers could easily occur. I do think high pressure will be to our west or close to our west for more of this period.

Overall I expect slightly above-average sunshine, somewhat below-average rainfall and slightly below-average temperatures.

Confidence level of 80% – main issue is where high pressure sets up for the second half of March.

April

Again April looks likely to be dominated by high pressure – again there are questions over positioning.

The first half looks more likely to be fairly mixed – there is a signal for both warm southerly winds and cold northerly winds – both involve high pressure close by, so we should end up with interchanging cold/warm spells, with some heavy showers around but more emphasis on sunshine.

Later in April, there are suggestions of high pressure migrating west/north a bit, allowing a cooler and somewhat cloudier north-westerly flow to become more dominant – some showers again but more emphasis on dry conditions overall. Again high pressure position probably varying so some short warm spells could easily be mixed into the dominant cooler, cloudier pattern through this spell.

Overall I expect average sunshine, somewhat below-average rainfall, average temperatures.

Confidence level of 70% – again the positioning of high pressure systems is the tricky thing to capture, and possible that it may be a bit warmer at times than I’m forecasting.

May

Again May will see high pressure over or close to the UK for much of the month – and by May there will be less cold air around to tap into so it should be warmer than average for most of the month.

The first half should be warm and sunny for most of the time – some variations, the odd weak weather front may cross from the north-west bringing some light rain and cooler conditions as high pressure moves around a bit – there may be some dull and cloudy days mixed in too depending on wind direction, but generally the theme will be warm and sunny.

Later in May, low pressure to the south will increase the chance of heavy showers and thunderstorms developing – though it likely remains warm or very warm and sunny most days, some days will see those heavy showers or thunderstorms later in the day.

Overall I expect above-average sunshine, below-average rainfall (unless you get a particularly torrential downpour in the latter part of May) and above-average temperatures.

Confidence level of 75% – again high pressure positioning is the tricky part and certainly possible I’ve over-egged the warmth.

And summer?

Well, that will depend on how La Niña pans out.

Early suggestions are that June will be sunnier and warmer than average – but some unsettled spells too.

There are signals that July and August will be fairly changeable with more rain and showers than normal – and temperatures generally suppressed for summer – though with short heatwaves likely.

Summer is a long way away though, and there is plenty of time for these signals to change.

So your overall take from this should be a drier than normal spring, a sunnier than normal spring, a colder than normal March, mixed temperatures April and warmer than normal May.

Roll on the first weekend where I can sit in the garden and have a beer.

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