Seasonal Forecast – Spring 2020

[Note that this is not a new forecast – this was issued at beginning of March. I just wanted to ensure that it displays on the site, and have also had a couple of requests to do so!]

Welcome to my Spring 2020 Weather Forecast.

I’ll start with a word of caution. I remind you that I am not a professional meteorologist (I’m a software engineer in case you wonder!) and seasonal forecasting is experimental.

For winter, I went for a mostly mild and unsettled winter, alas I predicted a dry February – and it has been the absolute opposite. At least I suggested wintry showers to end.

So some of this forecast will be wrong. Hopefully I’ll get far more right than wrong.

Also I request that you put a bit of work in now – just a share, retweet, whatever you fancy to say thank you for the work I put in. I don’t ask for much!

And thanks to Rachel for the spring-like photograph.

There are less background signals available for spring forecasting – well, they are available but they have less impact.

Most notably is the still very strong polar vortex, which will help to promote a westerly-based flow, at least for the first part of spring.

At some point during spring this will recede, and after winters with an undisturbed polar vortex (ie no major sudden stratospheric warming events) there is a higher chance of a more notable final warming event of the stratosphere.

A notable final stratospheric warming event would likely mean a notable cool, showery spell, potentially with Arctic air, for around 2-4 weeks, would be likely. Impossible to be sure, but I’m factoring this chance in.

I do also wonder if a notable final warming event subsequently leads to greater oscillation of the jetstream, therefore allowing for more extreme temperatures to follow…a theory I have but not seen any research to back up or dispute this.

Otherwise, El Niño is neutral so no effect, and I’m not sure there is much else in the way of other background signals that will have an impact.

I do expect our summer friend, and snow-lovers enemy, the Euro high, to often be present to our south/south-east – which is pretty much the ideal position for high pressure if you like warmth.

March starts with a southerly-tracking jetstream and fairly mixed conditions. Some showers or rain at times, and with colder air in the mix, some sleet or even snow could be mixed in – though more dry days than of late.

High pressure will be starting to have more influence, and by the middle of the month will be reasonable dominant – yet varying in position so there will be a mix of mild days and chilly days depending on wind direction, some showers and still possibly wintry showers. We could easily see days with maximum temperatures of 7’C and 17’C fairly close by. Also some frost and overnight fog.

For the latter third of March, it should be mostly dry, and high pressure should be in a favourable position for some warm sunshine most days. I’m fairly hopeful that we’ll reach 20’C before month end.

Overall I expect somewhat below average rainfall, somewhat above average rainfall and temperatures to balance out slightly above average – though with quite a wide range of temperatures through the month.

Confidence level 65%.

April looks like starting warm, sunny and dry – with high pressure either over the UK or a bit to our south-east.

The second half of April probably a bit more mixed, with some showers and perhaps a bit of cooler weather mixed in – but still quite often on the warm and sunny side.

There is a risk of a strong final warming of the stratosphere bringing something more notably colder and unsettled towards the end of April.

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

Around 70% confidence.

May looks more mixed to start, perhaps arguably the more unsettled part of spring – with the aforementioned risk of a strong final warming of the stratosphere bring a higher than normal chance of northerlies…but timing of this is a total guess.

Again towards the end of the month, I expect our Euro high friend to promote much warmer conditions, perhaps quite hot – though with a chance of some downpours or thunderstorms developing.

Overall I expect slightly above average rainfall (though dependant on catching some downpours…there could be wide local variations), around average sunshine and temperatures averaging out above average – but like March, quite a range of temperatures.

Around 60% confidence.

So, not bad at all – if I, and the long-range models that I trust are correct.

A look ahead to summer?

Currently I’d suggest that summer, particularly June and July will see some hot or very hot conditions at times – but there are no signs yet of prolonged settled conditions.

Above average rainfall currently looks like the more likely outcome for summer as a whole, perhaps more widely unsettled for August but that is a very weak signal.

June and July currently look favourable for Spanish Plume events – 2-3 hot days, becoming very humid with thunderstorms breaking down – and repeat.

Europe could well see more heatwaves with some hot, dry conditions expected to dominate.

These are just early summer thoughts and my thoughts are bound to change at least somewhat.

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