What’s Driving Our Weather + Winter Forecast

December 29, 2012

Weather Forecasts


I hope everyones had a great Christmas! After a short break from forecasting over the Christmas period I thought I’d kick us back off with a bit of an explanation over the reasons behind our current mild/wet weather, the lack of any real cold and how this compares to the winter forecast.

I stated in the forecast that December would likely be below average, after a very cold start things become quite mild and we’ve seen some extensive rainfall which has lead to some flooding for some. The overall December temperature is therefore likely to end up very close to the seasonal average or perhaps even slightly above. I’m sure you’d agree not the best start to the winter forecast.

The reason for our wet and mild weather is down to how the Polar Vortex split earlier in the month. You’ll remember that all models were forecasting a very blocked setup with High Pressure to our North only for this to go wrong at the last minute.  Up until now the Arctic Oscillation has remained very negative with high pressure over the Arctic, unfortunately a fragment of the polar vortex ended up being on our side of the Arctic and this has helped strengthen and maintain the Jet Stream over us keeping colder weather away.

The Arctic Oscillation is expected to become more positive into the new year

The Arctic Oscillation is expected to become more positive into the new year

It could be argued that the overall pattern in the winter forecast for December was correct, there has been a lot of blocking around we’ve just unfortunately been able to benefit from it and get the cold into the UK. The weather for the UK however has been completely different, unfortunately due to the way the Polar Vortex split earlier in the month.

There are signs that we’re finally going to see High Pressure building over the United Kingdom during the first week of January finally giving us some much needed drier weather.

8-10 Day Height Anomaly Chart showing high pressure over the UK

8-10 Day Height Anomaly Chart showing high pressure over the UK

GFS Ensembles showing things turning both milder and drier as high pressure builds

GFS Ensembles showing things turning both milder and drier as high pressure builds

Currently there are no signs of prolonged cold appearing on the models, but if we take a look at the Polar Stratosphere temperature profile we can see that we’ve seen a couple of warmings in the last couple of weeks.

Polar Stratosphere 30MB temperature profile

Polar Stratosphere 30MB temperature profile

This warming signal continues into the forecasting charts too. So I think as we move into the New Year things will become drier and for a time milder too, overnight mist and fog might be a problem under light winds and clear skies as high pressure influences our weather. Temperatures during the first part of January are expected to be mostly above average though perhaps cooling towards the middle of the month back towards the seasonal average.

Through into the second half of January, taking into account the recent Stratospheric Warmings and continued signal for these warnings I am currently expecting to see things cooling further as we see a more blocked pattern beginning to develop, perhaps finally bringing the first significant spell of cold.

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2 Comments on “What’s Driving Our Weather + Winter Forecast”

  1. guyfawkes Says:

    How likely is the cold spell?

    Reply

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