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The rest of December


19/12/2017

The first half of December

Provisionally to the 17th December the Central England Temperature (CET) is +3.9C which is exactly 1.0C below the average. On Sunday 10th December heavy snow fell in parts of southern and central Britain with depths of up to 30cm recorded. Northern regions have also seen snow at times in form of showers and there have been some very cold nights with temperatures falling as low as -13C (9F).

Heading towards the New Year

As we head towards the New Year a major change in the weather is set to take place. A much more mobile pattern is expected to develop across the North Atlantic as the jet stream strengthens. That will lead to a succession of low pressure systems moving in from the west towards the UK. With the jet stream dipping southwards there is the likelihood of temporary incursions of colder air, but in general temperatures are expected to be close to the average for much of the period. Higher nighttime values could pull the CET up towards the average by the end of the month if things develop as computer models currently show.



Computer ensemble analysis

The postage stamp chart shows pressure pattern forecasts from each of the 19th December GEFS 00z ensemble model runs on Friday 29th December. The UK is in the middle of each plot predominantly under blue or purple shading. That indicates low pressure and westerly winds which in the UK is usually means quite mild conditions. Some of the runs show very deep areas of low pressure suggesting stormy conditions and that is something that needs watching during the holiday period.

GEFS 00z pressure and 500hPa postage stampsmax temperatures

Summary

The first half of the month brought a lot of cold weather with heavy snow in places. A transition to unsettled weather is forecast to develop in the run up to Christmas and continue until the end of the month. Temporary colder incursions of air remain possible but in general the Central England Temperature is expected to recover back towards the average by the end of the month.

TWO monthly forecast for December

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