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Weather updates from site founder Brian Gaze that keep you in the know.


Cold and unsettled

Posted Tue 3rd December 12:16

The current spell of quiet and chilly weather will gradually give way to more unsettled conditions later this week. It is also set to turn milder for a time. Next week a more wintry flavour is expected.

Snow on the way?

Computer models are showing quite a mobile pattern across the North Atlantic next week. The jet stream dips southwards again leaving the UK on its cold northern side. With weather systems tracking farther south than usual there is an increased risk of sleet or snow. However, conditions will probably be marginal and in the south rain is more likely for much of the period. There risk of snow is greater in the north and disruptive amounts are a distinct possibility. 

Could heavy snow also affect southern counties? It is possible but at the moment I think the chance is relatively low. This morning's GFS 06z run shows snow depths reaching an incredible 56cm by Saturday 14th December to in parts of Surrey and Hampshire. I'd be amazed if this happens!

GFS 06z snow depth forecast

The GFS operational run often predicts more snow than most of the other computer models. In my view that tendency has been amplified since its upgrade earlier this year.   

A more balanced view

To put some context around next week's prospects it is worth taking a look at the London GEFS ensemble plot. What it shows is:

1) Rather cold conditions during the middle third of December

2) The snow row value which can range from 0 to 23 peaks at 5 which roughly equates to a 22% chance

3) The risk of precipitation continues indicating an unsettled period 

London GEFS 06z plot

So it suggests chilly and unsettled weather in the south next week with a low to moderate chance of it turning cold enough for snow to fall. Remember the snow row makes no attempt to assess the likelihood of accumulating snow.

Comparable plots for more northerly locations in the UK show a high percentage chance of snow. That's what you would expect to see when the flow is coming from the northerly quadrant. 

TL;DR

Unsettled and rather cold weather is expected next week. A northwest to northeasterly flow is forecast for much of the time so the lowest temperatures will be in the north. That's also where the greatest risk of snow is and the potential for some very heavy falls exists, particularly over the hills.

In the south parameters are expected to be more marginal and for much of the time rain rather than snow is likely. Nonetheless, the GEFS currently suggests a 22% chance of snow in the south so it is worth keeping a close eye on developments. 

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