TWO Buzz

Weather news and views from Brian Gaze.

Snow risk this weekend

Colder weather expected

Posted Tue 24th March 16:15

A change in the the weather is expected during the second half of the week. High pressure building in the mid-Atlantic will allow much colder Arctic air to sweep southwards across the UK. The risk of snow probably increases.

Turning colder

The London GEFS 06z plot below illustrates things well. Upper air temperatures shown on the top half of the plot tumble this weekend. Most of the runs in the model show them falling to -10C which is a marker for a very cold spell in the winter. I don't think they fell to this level at all in December, January or February.

At this time of year the sun is much stronger so daytime temperatures will rise in the sunshine. However, very cold nights are likely and when showers come along during the days temperatures will tumble. At night temperatures could fall to -5C (23F) in frost pockets in the south and possibly -10C (14F) in the northern valleys and glens. 

The snow row count reaches 19 and 20 on successive days. It counts the number of model runs forecasting falling snow with the maximum value being 23. Therefore, I'd not be surprised if even southern counties see a few flakes of the white stuff this weekend. Accumulations are most likely over the Welsh mountains and the Peak District.   

GEFS 06z London 24th March 2020

Snow risk this weekend

The GFS 06z chart below shows forecast mean surface level pressure and 850hPa temperatures. High pressure is centred to the northwest with the UK sitting under a cold northeasterly flow. In the east 850hPa (about 1500m above sea level) temperatures are down to -10C which is indicated by the blue shading. Solar heating and the deep cold pool have the potential to trigger a lot of showers. 

GFS 6z 850hPa temperature forecast, issued 24th March 2020

The GFS 06z precipitation type forecast chart for 15:00GMT on Sunday 29th March is below. The GFS is notorious for over predicting the extent of the snow risk. Nonetheless it gives some indication and suggests that many of the showers will have a wintry flavour to them.



Northern Ireland and western Scotland which are closest to the high pressure centre have mainly dry conditions.Virtually anywhere else could see rain, sleet, snow or hail falling from the sky at times on Sunday!

GFS 6z 850hPa snow forecast, issued 24th March 2020

TL;DR

Cold Arctic air is expected to plunge southwards across all regions later this week. By Sunday the risk of wintry showers  may be widespread and even parts of the south could see snow falling to low levels. Nights will be very cold with widespread and sharp frosts where clear periods develop.   

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