Seasonal Forecasts

Autumn Weather Forecast 2020

Welcome to my Autumn Weather Forecast 2020.

I always have mixed feelings about autumn. A relief that heatwaves are unlikely. An excitement about the potential for proper rain and wind! Sadness for the diminishing amount of daylight. And I enjoy the colour of the changing leaves – it can be such a photographic season.

First the admin. If you appreciate my forecasts, I ask you to share occasionally, use the “invite friends” button on Facebook, post on social media, send to your family/friends. It is all I ask.

Next, thank you to Ros for the photograph. There were 3 or 4 really strong contenders, but I was really keen on the fact that it offers both sunshine, and threat of rain – at least clouds, a bit like the autumn I’m expecting. A £10 donation to The British Heart Foundation has been made as a thank you.

Finally a reminder that seasonal forecasting is really rather difficult. There are some background signals to assist but it is quite speculative. Some of what I forecast will be incorrect, do not take it as gospel. The hope is to get more right than wrong, and the general picture.

Feel free to check my summer forecast – I thought that it went really well and am happier with it than most seasonal forecasts in the last couple of years.

Background Signals

So the main background signal that informs my forecast is that of La Niña, which is developing in the Pacific Ocean. Likely to be a fairly weak affair, I still expect this to increase the general westerly flow over the UK, increasing the chance of strong winds and rain overall.

However I expect the mean jetstream flow to be a little north of Scotland, on average through autumn, so for those of us in the south of the UK, this will mean high pressure loosely in control – often a similar pattern to July, where we swapped short spells of high pressure though often cloudy, for short unsettled spells – the westerly flow in July meant that temperatures were not hot, bar the last day of July.

September

September is always a tricky month to forecast as Atlantic hurricanes can change previously expected weather patterns, or sometimes exaggerate current patterns. It has been a busy hurricane season so far, though we’ve only had the remnants of one ex-tropical storm and that had no effect on our weather patterns, at least that I could ascertain.

So there is always that bit more uncertainty for September.

The first two weeks of September I expect to be broadly fair. Some sunny days, some occasional showers or fairly weak bands of rain. Some warm days, some with more average temperatures.

Around the middle of September, it looks like cooler air with spread down from the north-west, with rain, showers and strong winds.

Then the last week, maybe 10 days, seeing something more settled, though still fairly mixed with the odd weather front – but more dry days than not, some decent sunshine and some warm, perhaps very warm days.

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

Confidence level around 65%.

October

At the moment I expect October to start with some decent spells of settled weather, likely rather warm with high pressure close to our east allowing for a more southerly or south-westerly flow – though chance of fog overnight.

During the middle portion of the month, we should see more in the way of weather fronts bringing wind and rain at times, but still some fine and dry weather mixed in. Temperatures around normal.

Suggestions that the month may end more deeply unsettled, but this is probably the most uncertain part of the forecast.

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

Confidence level around 60%.

November

No particular weather type expected to dominate in early November. I do expect the jetstream to be bringing wet and windy weather to Scotland – and some of this will drip down our way with some weather fronts, some windy days, mixed in with fine days and temperatures generally around average, though perhaps a tad chilly in any lengthy settled spells where frost and fog will be possible.

For the latter part of November, the general mixed theme remains though with more of a south-westerly flow, and something milder – though rain and wind that bit more often than early November.

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

Confidence level around 65%.

Winter?

Well, December is a long way ahead. With La Niña I’d expect a wetter winter than normal and with the jetstream further south, so we’ll get more of the brunt of weather systems than during autumn, where Scotland should get the brunt.

That said there are plenty of background signals that suggest a good chance of cold spells. Then again, there were a few last season and look what happened!

So I’m fairly confident of a wetter winter than normal. For chances of cold spells and snow you’ll have to wait until nearer the time.

Seasonal Forecast – Summer 2020

Right. Welcome to my Summer 2020 Weather Forecast.

Let’s start with the caveat. I am not a professional meteorologist and at least some of this forecast will be wrong.

The aim is for more to be right than wrong – and my Spring 2020 forecast went pretty well. Not perfect – that is impossible. But I’m certainly happy with it, I think it was the most successful seasonal forecast for a year or so.

Also this is where I ask you to do some work. I do these forecasts for free and the only thing I ask in return is an occasional share. Share on Facebook, Twitter, Reddit, Mumsnet, Lycos Chat Rooms, whatever your internet poison of choice is. There are links to donate on my website, but I seriously don’t want or expect anything – if you feel thankful then maybe give to charity instead…there are people going hungry and I eat too much…but if you insist on doing so the option is there.

And thanks to Louise for the photograph. I had 150+ photographs, I could easily have used 130+ of them…and some really astounding ones. Out of my very favourites, this was the one that told the story most closely.

A £20 donation to the charity of her choice will be upcoming…please get in touch if you are reading!

It does look like a good summer ahead (unless you want cold and wet), but there will be a fair mix of conditions along the way.

Background Signals

Lets start by looking at some background signals.

The main one that I have my eye on is the sea surface temperatures. Anomalously warmer than normal near us – and colder over the west Atlantic. I feel that this will be the main background signal for our summer, and this should help with high pressure building either over the UK or to our east.

It looks like La Niña might develop later in the summer or early autumn, which a month or so ago I thought would develop around July and bring a cooler and wetter end to summer – now it looks more likely to develop during August/September and even then there is uncertainty. So I’m mostly discounting any effect – but this explains my original thinking of an unsettled August which I am now thinking unlikely.

The Quasi-Biennial Oscillation (look it up if you want to be scared by maths) is heading into easterly phase which can help promote high pressure to our north – but this transition is wobbling and perhaps showing signs of going back westerly which it absolutely should not do for a couple of years. Odd and concerning, but as far as the summer goes, this again helps my confidence that summer may end warm and sunny. I was originally expecting that this could increase the chance of unsettled and cooler conditions towards the end of summer, but the wobble makes me think not.

We are at a solar minimum which I feel favours weather patterns to get stuck in situ more easily – so things take longer to change…hence the long sunny spring. The science on the effect of solar minimum is debatable – it should in theory have favoured a cold winter in 2019/20 and look what happened! Though the record (?) strong Indian Ocean Dipole just overrode all other signals it seems.

The lack of heat over the continent so far this year and relatively wet conditions to our south suggest to me a lower chance of extreme heat – so a lower chance of record temperatures being broken, but it certainly can still be hot or very hot at times.

I also expect a busy Atlantic hurricane season. Whilst I have no idea how this might play out and affect our weather this far in advance – think of it as a greater curveball to my forecast than usual. When hurricanes get this far east (being ex-hurricanes by that point), they can change weather patterns – or exacerbate them. 2011 (I think) was a classic where two ex-hurricanes passed to our north-west bringing us that really hot September.

So…tell me something I understand

The general pattern for June will often see high pressure to our west, and also to our east over Russia – with us stuck in the middle, occasionally enjoying an extension of either high pressure, but low pressure dominating to our south.

June starts very warm (granted I’m writing this on 6th June so easy to forecast for the past). A northerly flow develops, bringing cooler and showery conditions for a while.

Exactly what happens after is uncertain, but rain or showers are quite likely in the second week or June – and rain bands could get stuck somewhere over England and produce some large totals of rain…but whether that is here or somewhere else I cannot know at this stage.

I feel that an easterly flow may develop before the middle of June – bringing warmth but an increased risk of thundery downpours.

Later in June looks more likely to be warm or very warm, perhaps even quite hot at times. Some good sunny days but I’m not expecting wall-to-wall sunshine and some thundery showers or even rain should be mixed in.

Certainly an interesting month, and watch out for the potential of flooding in France and/or Spain.

Overall I expect around average sunshine, somewhat above average temperatures. Low confidence on rainfall as it will depend on whether we get stuck under bands of rain in the second week of June, and any potential downpours.

Confidence level 70%.

July (I will write less, I promise), again looks quite a mixed month. There is a danger that I will get timings wrong on things here especially, but here goes.

There is a weak signal for something cooler and showery for the beginning of July again.

Otherwise July looks like a mixture of fine, very warm/quite hot sunny weather, with occasionally weak weather fronts from the north/north-west bringing some less warm conditions and a bit of rain/showers.

Towards the latter part of July, it looks like high pressure will be close to our east and low pressure close to our west – there should be some hotter and more humid days around, but also some wet days too, perhaps some thunderstorms.

Overall I expect slightly above average sunshine, above average temperatures and rainfall slightly below average – though catch a thunderstorm or two and it could locally end up well above average.

Confidence level 50%.

August now looks like high pressure will dominate to our east or over the UK and low pressure to our west. This distance away it is still finely balanced and I wouldn’t be surprised to see a wet August, but my forecast is for a sunny and hot August.

Yes, August I expect to be the best of the 3 summer months and I don’t recall ever forecasting that! Though I barely remember last week let alone every summer forecast I have made.

Often very warm or hot, good sunny days – occasional heavy, thundery showers developing some afternoons, though plenty of very nice weather.

Towards the end of the month, unsettled conditions arguably more likely as we head towards September – and the potential influence of La Niña.

Overall I expect above average sunshine, above or even well-above average temperatures and rainfall again more likely below average, but could be above locally if you catch some downpours.

Confidence level 60%.

Happy with that?

A brief look ahead to autumn – September looks more likely to be unsettled, otherwise there are no strong signals for the rest of autumn – a very weak signal for a drier than normal October.

I’m not thinking about winter until I know how the Quasi-Biennial Oscillation progresses.

Go on then – get sharing!

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.