Snow and frost expected

Snow risk varies through the week

Snow is likely to come from both showers and longer outbreaks. Showers are most likely in northern Britain and northern-facing coastal counties, due to the northerly wind direction. However, areas of low pressure pushing eastwards across the UK will bring the likelihood of longer outbreaks of rain, sleet, and snow. The snow risk is on the northern and possibly western flanks of these low-pressure systems. On their southern side precipitation will fall as rain due to the air being much milder.

Monday and Tuesday

The areas of low pressure being modelled are relatively small features, especially when considered on a global scale, which is the perspective of medium-range computer models. Therefore, predicting their exact track is difficult, as various computer models show different scenarios. However, as their arrival time nears, two things happen:

1) Global models align with each other

2) Higher-resolution models, which focus on smaller areas like northwestern Europe or the UK, cover the time period in question

In recent days an area of low pressure has consistently been forecast to push eastwards across the UK early next week. The pressure chart below shows it centered near northern Wales and northern England at 18:00 on Monday, November 18th.

As noted, snow would be expected on its northern flank. The chart below illustrates this, with pink shading showing snow. The other colours highlight rain of varying intensity.

The scenario here appears the most likely one, with snow mostly in northern England, southern Scotland and possibly Northern Ireland. The Pennines could expect to see substantial falls, possibly between 10cm and 20cm, but snow could cause disruption at low levels too.

It is still too far away to be confident about the track of the low pressure and some computer models take it a little farther south. The chart below illustrates this, with the snow risk extending down into central areas. 

It is also possible that rain will turn to sleet and wet snow for a time on its back western edge. Therefore, even some locations in the south could see falling snow, but accumulations would be much less likely due to wet ground and the quick return of drier conditions as the low pressure pulls away eastwards.

Snow risk moves southwards later?

A second area of low pressure is being modelled for later next week and there are signs of it taking a more southerly route. In turn that would mean the risk of snow heading further south as well, although it is important to bear in mind that it is very early in the season and conditions could be very marginal. Snow is much more likely in January, February and March than it is in November.

The chart below shows the low pressure pushing eastwards across France, with the northern extent of the snow close to London.

It will be a few days before the details firm up and it is possible the low pressure will take an even more southerly route. Were that to happen, the rain and snow would completely miss the UK leaving mostly dry but cold or very cold conditions.

Severe frosts are likely

The other key feature of the weather next week is that frosts are expected to become widespread and in places severe. The chart below shows forecast minima on Tuesday night into Wednesday morning.

The combination of snow cover and long nights gives the potential for some very low values. There are no suggestions the November record of -23.3C set at Braemar, Aberdeenshire on the 14th in 1919 will be challenged. Nonetheless, it is possible -10C to 15C could be reached in the Scottish glens next week.

When will milder conditions return?

Milder air may return around 23rd November in southern Britain. However, at this range forecast confidence is very low. In general terms the favoured outcome is that the milder conditions will push in from the west or southwest, with northern Britain remaining in the freezer for the longest. Also, there is the possibility of a period of transitional snow close to the boundary between the cold and mild air masses. 

If the wintry spell lasts as long as computer models are suggesting, this could be the most notable November cold period since 2010. That was followed by the coldest December for 100 years and became the first month since February 1986 to record a sub-zero Central England Temperature (CET) average.

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