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Posted Wed 30th January 2019 18:32
An area of low pressure tracks to the southwest of the UK towards the Bay Of Biscay during Thursday and Friday. Weather fronts associated with it push northeastwards across parts of the UK and they bring a risk of rain, sleet and snow. Disruptive accumulations of snow are expected in places, but amounts probably vary a lot and there is still uncertainty about the northern extent of the risk.
I'll quickly run skip through some of this afternoon's computer model runs to illustrate where snow may fall and how much there could be. I'll repeat the health warning from earlier this week: The computer models update every 6 or 12 hours and even at this late stage the situation is an evolving one.
The American GFS model is once again very liberal with its snow predictions. As I noted in my last post, this model isn't the best one to identify local variations. Nonetheless, I have seen it perform better than some of the higher resolution ones in the past.
The chart below is for 18:00 GMT tomorrow. Heavy snow is affecting Wales and much of southern England with rain in the south western peninsula.
Step forward to 21:00 GMT and you'll see the area of snow has continued to march northwards and eastwards. It reaches Yorkshire and Lancashire which is further north than most models are predicting. In southern counties drier weather has returned and a frost would be expected.
The German ICON shows a more granular level of detail than the GFS. As well as providing precipitation rates, the models often provide a snow depth forecast. I'm not a big fan of them and think they are more accurate in continental climates where parameters are less marginal.
Having said that I'll use an ICON snow depth chart on this occasion because to me it appears reasonably representative. Ignore the snow totals shown in the the north because I think the run was initialised with them. If it's correct the heaviest falls will be in South Wales where accumulations reach 17cm. A covering of 3cm to 5cm is expected in much of southern and central England too.
The KNMI Hirlam model shows a similar pattern Icon but snow depths are a lot lower. The chart below is for 22:00 GMT tomorrow night and the following steps have the snow fading away and edging southwards.
This afternoon's Meteo France Arpege run also keeps the snow further south than the GFS. The northern extent is the Midlands and again the heaviest bursts are in Wales and central southwestern England.
The chart below is for 23:00 GMT. Later steps show the snow fizzling away and not progressing any further northwards.
The Canadian GEM model run also is also reasonably consistent with Arpege and Icon. The chart below is for 21:00 GMT and subsequent steps shows the snow becoming lighter and patchier.
The charts from the 5 different models give an idea of the which areas are likely to see snow tomorrow. GFS is alone in taking the risk as far north as Yorkshire and Lancashire. The other models have the snow reaching the Midlands tomorrow evening and fading away by Friday morning.
The heaviest falls may well be in southern Wales, the west Midlands and parts of the south west. Accumulations of over 10cm are possible locally, especially over high ground in southern Wales. Lighter falls of snow are likely in more eastern parts of southern and central England with accumulations of several cms possible.
On Friday it remains cold. There could be further wintry showers in the north west and near the east coast. In the south any outbreaks of snow left should fade away to leaver dry conditions.
PS: To view the latest charts the easiest way is to follow the link link below and select the model you want.
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