There’s been a lot of talk on various internet weather forums of something brewing for the second half of the month and some have even started to say a period of extreme cold is on the way.

Unfortunately there’s not a whole lot to support this idea within the weather model outputs, although there are signs things could potentially turn colder as we move into the second half of the month. But before I talk about that I’d like to talk about the Polar Stratosphere for a second.

You’ve probably heard the term Sudden Stratospheric Warming or (SSW) being thrown about, when sudden and major warming occurs across the Polar Stratosphere this has a tenancy to reverse zonal winds across the pole which in turn weakens the Polar Vortex giving rise to increasing amounts of Northern Blocking.  A SSW is forecast to begin on Sunday, the following charts show this.

This chart shows a reversal of the mean zonal winds across the Arctic
This chart shows a reversal of the mean zonal winds across the Arctic
This chart shows the temperature in the Polar Stratosphere. We can see the warming indicated by the yellows and oranges
This chart shows the temperature in the Polar Stratosphere. We can see the warming indicated by the yellows and oranges

There is however a lag effect between warming and surface conditions here in the UK. It’s also important to remember that compared to the Northern Hemisphere the UK is a very small corner and SSW does not always guarantee colder weather for the UK, however it does increase the chances of colder weather developing.

Back to the potential for colder weather towards the middle of January – At the moment there are tentative signs that this could be the case but as usual there’s a lot of uncertainty over how things are going to develop / how cold things could get. Take a look at the GFS Ensembles below

GFS Ensembles show a large amount of scatter beyond next week suggestions huge uncertainties in the forecast
GFS Ensembles show a large amount of scatter beyond next week suggestions huge uncertainties in the forecast

Whilst the temperature is on a downward trend, the mean doesn’t really fall very far below the seasonal average and there is a huge amount of scatter within the ensembles. This suggests that quite a few different solutions are possible and it’s hard to pick out a definitive trend.

Likewise, the ECM ensembles show a cool down to around average but little sign of anything significantly cold just yet.

ECM Ensemble mean showing a huge amount of scatter suggesting uncertainties in the forecast
ECM Ensemble mean showing a huge amount of scatter suggesting uncertainties in the forecast

The ECM ensemble mean in fact, is far from cold with a South or South-Westerly airflow across the United Kingdom.

ECM ensemble mean suggests milder South-Westerlies as opposed to colder Northerlies at this stage
ECM ensemble mean suggests milder South-Westerlies as opposed to colder Northerlies at this stage

Conclusion:

There’s too much uncertainty within the ensemble models to be able to forecast this period with any accuracy at all. The Sudden Stratospheric Warming is definitely a good sign if you’re looking for colder weather, but at this stage it’s impossible to say whether it’s going to have that effect for us here in the UK.

Temperatures look likely to return to average as we go through the course of next week but beyond that, there really are too many possible solutions on offer to speculate which way it’ll go.

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