Welcome to the winter weather forecast 2024/25 for Reading & Berkshire.
Firstly the usual caveats – seasonal forecasting is difficult, no seasonal forecast will ever be 100% correct, as it is bound to events on a local and global scale.
Seasonal forecasting is done mostly on a global level, and also thought of in monthly terms – for example, the background signals and long-range models could suggest higher than normal pressure is likely one month, but that wouldn’t stop one week or more being under low pressure, and wet.
So you should always expect any seasonal forecast as a rough guide at best, and remember that I’m not a professional – just an amateur forecaster with a half-decent grip on what models are suggesting, and a decent writing ability.
My autumn forecast was…alright…I picked some things out correctly, for example the greater chance of northerly flows than normal in November, but then I also picked out a wet start to November, and it was dry.
Also a massive thanks to those who sent photographs in, and more so to those who do on a regular basis.
Thanks to Clare who’s photograph I’ve chosen – a small charity donation will be sent as a thank you, please let me know to whom.
Background Signals
Winter always has more impactful background signals than any other season, but that never is the whole story – events do and will deviate from this.
The Quasi-Biennial Oscillation is currently in westerly phase, which increases the chance of westerly winds, and hence milder, wetter conditions.
La Niña, though not the strongest, does tend to increase the chance of northerly flows in autumn and early winter (as we have already seen).
Sea surface temperatures around most of the UK, and especially to the west, are warmer than normal – so this will mean temperatures more likely to be higher than normal. However, to our north, sea surface temperatures are colder than normal – so northerly flows may have more impact in terms of cold than normal.
The Indian Ocean Dipole is forecast negative for the start of winter, which can increase the chances of colder northerly flows.
Finally, the Madden Julien Oscillation, which is only helpful (questionably so in my view) over the more medium-term, currently is forecasted to end up in phases which favour cold weather later in December.
A sudden stratospheric warming event (SSW) cannot be discounted, which is where the stratosphere (the atmospheric layer above our troposphere) suddenly warms, which can break apart the polar vortex and cause cold weather to flood down in our direction – the Beast From The East in 2018 being the classic example.
However, we had 3 such events last winter, a once in 250 years occurence – the first two arguably gave us much milder and wetter conditions, as the cold air from the Arctic, if I remember correctly, flooded south but to our west – and hitting the (relatively) warm Atlantic ocean caused large areas of low pressure – and the mild/wet conditions. And also caused the latter part of my winter forecast to fail!
And the third happened in March, too late for wintry weather but then caused a cooler than normal spring.
I’ve read arguments that La Niña combined with a westerly QBO increases the chance of an SSW occurring over winter…which is what we have. But not sure what to make of that.
So quite a lot of different background signals, but definitely some patterns including increased chances of northerly flows in early winter – as such it is time to start the forecast.
December
December looks a very variable month, especially to start. It should settle down after the first week, with temperatures around normal or a little below, though some showers possible in the easterly flow. Frost/fog will be possible.
After mid-month, something more changeable looks more likely with further heavy rain and strong winds at times – chances of more named storms, though temperatures most of the time above average – short colder snaps still possible.
Towards Christmas and into the New Year period, colder northerly flows become more possible, though westerly flows could still dominate. Expect changeable conditions, wind and rain at times, some sunnier and colder days too. Again, quite a mix seems most likely, though perhaps veering towards dry more than wet.
Overall I expect above average rainfall, around or slightly below-average sunshine, around average temperatures.
Confidence level 80%.
January
January again looks a fairly mixed month. The start of the month has greater chances of drier and colder weather, before becoming unsettled once more. Northerly flows very possible, named storms very possible.
In the second half of the month, something milder and changeable seems more likely – some rain at times, but also some dry spells, if perhaps cloudy and dry.
Overall I expect around average rainfall, slightly below-average sunshine, and slightly above-average temperatures.
Confidence level 60%.
February
Suggestions for February see higher than normal pressure over Europe, so something milder and drier than normal seems the more likely general outcome for the first half of the month – though some weather fronts will likely get through to bring some rain, albeit more limited amounts.
More likely it stays mild or very mild in the latter half of February, with dry conditions more likely than wet.
A sudden stratospheric warming event would increase the chance of cold and dry for February, considerably…but this is impossible to know at this stage.
Overall I expect rainfall to be below average, sunshine around or slightly-above average, temperatures above average, though with some uncertainty towards the end.
Confidence level 50%.
Summary And Early Spring Thoughts
So a pretty mixed winter seems more likely, though not quite as wet as it has been with high pressure playing more of a role than it has the last 18 months or so. Any cold spells more likely in the first 6 weeks of winter, and those from the north.
Early signs for spring, assuming no sudden stratospheric warming, are for a much warmer and drier first half of spring. Oh do hurry up!…