Welcome to my winter 2021/22 weather forecast for Reading and the surrounding areas.

This is going to be quite a long post…I guess I should pour myself a drink…it is nearly Christmas after all.

So let’s start with some admin as usual.

Firstly thanks to Grace for the superb photograph, and first clue to my expectations of the weather this winter. A £20 donation has been made to Blood Cancer UK.

Secondly thanks to everyone who sends in photographs more regularly, comments, shares, etc – you ensure there is still a point in me doing these forecasts.

Finally a reminder that seasonal forecasting is experimental. Though my understanding and the understanding of the general meteorological community improves every year, some parts of this forecast will no doubt be wrong.

I’m actually really happy with my autumn forecast which was surprisingly close to reality – I’m particularly delighted to have picked out the signal for the cold spell at the end of November, 3 months ago. That said, background signals were strong.

Background signals

Which is a good time to start talking about background signals going into this winter.

Unsurprisingly the background signals are conflicting and create quite a lot of uncertainty – arguably more so than usual. Yet there are plenty that point to a colder than normal winter – alas, the seasonal models generated by super-computers point to a mild winter. Which is why you may have heard professional meteorologists arguing different cases.

Of course, nobody knows exactly how it will pan out – some professional and experienced forecasters are going to be wrong. Maybe I will too.

Anyway, those signals:

La Niña. We had a La Niña last winter, and we have another one this winter. La Niña is thought to increase the chance of north-westerly/northerly flows in November/December, and milder westerly flows in January/February – hence why I was pretty confident of the current cold spell some time out.

It does also depend somewhat on the strength, and also where the La Niña is centred – this is more of an east-based La Niña which I believe increases the cold signal for North-West Europe, and can also increase the chance of high pressure forming to our north/north-east – which would suggest cold easterly flows are possible.

Madden-Julian Oscillation. The pattern of thunderstorms over the Indian and Pacific Ocean has an effect on our weather and the pressure patterns. This is more of a medium-term forecasting tool, so really only any use for December. Currently it is in phase 6, and looks like going into phase 7, which should promote high pressure forming to our north/north-east.

However, it is argued that MJO signals are often over-ridden in La Niña winters, so I’m not sure how much notice to take.

Quasi-Biennial Oscillation. These are stratospheric winds which switch from west to east, roughly every 22 months. It has recently switched to east which tends to encourage a weaker polar vortex and increases the chances of cold weather in Europe.

Said polar vortex is kind of disorganised in the troposphere (our level of atmosphere) at the moment, though has hints of organising. In the stratosphere (way above our atmosphere – the next level up) it is unusually strong. If the tropospheric and stratospheric polar vortexes couple, then you can wave goodbye to the chance of cold for weeks – sometimes even until the end of winter – and you’ll have weeks of mild, often wet and windy weather. There are hints this coupling may happen later this month, but is highly uncertain.

One thing that can break the coupling of the vortexes, is a sudden stratospheric warming event (SSW) which you’ll likely have heard me talk about in previous winters. These are a sudden warming of the stratosphere where the winds reverse fairly suddenly. What normally happens 2-4 weeks afterwards, is that high pressure blocking systems set up across the northern hemisphere and cold air floods down into the US, Europe and Asia – though not everywhere, as some places will be on the mild side of the blocking systems.

We had one in 2018 and ended up with the “Beast From The East” – a classic response from an SSW. However we had one last winter, and there was little effect on our weather – we had some cold weather that followed, but nothing unusual and arguably not because of the SSW. However, I do believe that the colder spring that we had was because of the SSW.

It is impossible to know if an SSW will happen more than a couple of weeks ahead. However, a pressure pattern is currently setting up over Europe/Asia that can be a trigger of one, say by late December/early January – so with the lag, that gives a slightly higher than normal chance of significant cold in February.

Finally, the solar cycle. I feel this is more debatable than most signals, but periods of low solar intensity like we are coming out of now, tend to encourage weaker polar vortexes and hence a greater chance of cold spells. And those winters where solar activity is just starting to increase, like this winter, are arguably most likely to experience this effect.

I guess you want a forecast now?

Hopefully you can at least you can see there are lots of conflicting signals, even if more of them do point to cold than normal. As such, overall I think winter will be slightly drier and colder than normal – though with some unsettled spells.

December

December looks like it will be a battle between an Atlantic Ocean finally waking up – and a blocking high stretching from Siberia to Scandinavia.

Generally it will be colder than normal, though low pressure systems will battle into the block, bringing wind and rain at times. There is a plausible chance that there could be some heavy snow as low pressure systems struggle as they come up against cold air to our east – but most precipitation should be rain.

After around mid-month, the jetstream should shift north, with high pressure building from the south – still some weather fronts but mostly light/patchy rain, overnight frosts and fog possible, though generally slightly milder than normal.

Then towards Christmas, that cold weather block to our east looks like it will migrate west, bringing colder air and a seasonal feel, with sharp frosts possible and cold, crisp sunny days. Snow showers would be somewhat possible though dry weather is expected to be dominant.

Overall I expect temperatures to be slightly below-average, rainfall slightly above-average and sunshine amounts around average.

Confidence level 75%. Main uncertainty is over the Christmas period – as it is certainly possible that we retain a milder southerly/south-easterly source and have mild, dry, probably cloudy/foggy weather instead.

January

January does look more unsettled with more influence from the polar vortex. Any early cold and dry weather should be shunted out of the way by a resurgent Atlantic, perhaps initially some snow as the milder air battles to displace the colder air, but generally becoming mildish and wet.

Occasionally the flow should be more north-westerly, allowing for colder weather, though nothing extreme, and brief easterly flows will also be possible – so though rain is the more likely outcome, there will be marginal opportunities for sleet/snow.

Also worth mentioning that the heaviest rain should often be to our north, so I’m not expecting the wettest month ever, but generally fairly unsettled with some short dry spells.

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

Confidence level 65%. Main uncertainty is the block to the east, and whether colder and drier weather could again spread west at times.

February

February currently looks likely to be a dry month with high pressure generally over the UK, or close to.

This does lead to some uncertainty on temperatures, arguably something milder/cloudier is slightly more likely early February, with colder than normal conditions most of the time after early February.

Often sunny though a risk of fog at times, regular overnight frosts likely which could be sharp, depending on the exact position of high pressure.

Rainfall will be limited, though occasionally the odd weather front will pass over bringing a bit of rain, perhaps sleet/snow, as the high pressure repositions itself.

Low confidence but there are suggestions of a very mild end to February being possible.

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

Confidence level 60%. Main uncertainty is the chance of an SSW, which would increase the chance of easterly flows and snow showers – I’ve assumed no SSW in the forecast as they are impossible to predict this far out.

Summary and Spring Thoughts

So, overall a slightly drier and colder than normal winter is expected, though with some notable unsettled spells too – especially in January.

Remember, it will be a shock if all this comes to pass, but hopefully it will be a good enough guide. Should an SSW occur, then there will be a good chance of a significant cold spell 2-4 weeks later, but it is impossible to know now.

Assuming no SSW (or an SSW that doesn’t favour cold in the UK), then early signs are that March could be warmer than normal.

However, don’t get too excited – early hints for April and May are for colder and somewhat wetter conditions than normal.

Well, I hope you enjoyed reading this forecast, I hope it is reasonably accurate and I hope you can enjoy the weather – whatever it throws at us.