27 Jan 2015

Snow and a bitter wind to end the week

The weekend just gone offered some respite from the cold, icy weather that gripped much of the UK last week – especially in the north.

However, winter is going to bite back in the coming days, with the wind eventually coming from a northerly direction.

This will allow cold, arctic air to flood southwards across the whole of the UK, bringing not only a bitter wind but the threat of snow, ice and travel disruption.gwynedd_snow_g_wp

As is always the case with forecasting snow, there is some uncertainty as to precisely how much will fall where, but there is increasing confidence about the most prone areas.

Jet stream diving southwards

The jet stream, a fast-moving ribbon of air around 30,000ft up in the atmosphere, not only drives our weather, but is also the dividing line jetstream_30thJan_WZ_wpbetween mild and cold air.

In the coming days, the jet stream is going to dive south of the UK, putting us on its colder side, causing temperatures to fall and the weather to take on a wintry flavour.

As it dives south of the UK, it will spin up an area of low pressure that will get stuck in the North sea, which will in turn act as a cog, dragging the cold air across us.

While the cold expected in the coming days is nothing exceptional for this time of year, it will feel bitter in a strong wind that will give blizzards at times over the mountains in the north, when combined with heavy snow showers.

How much snow will fall?

At the moment, Scotland, Northern Ireland and northern parts of England are the places most likely to see notable snow_warningTHU_MO_wpaccumulating snow, as this is where the heaviest and most frequent snow showers will be.

The latest amber ‘be prepared’ snow warning from the Met Office highlights that Scotland and Northern Ireland could see 5-10cm at low levels, away from coasts, between Wednesday and Friday, with more than 15cm over the hills and mountains.

During the same time, northern England is likely to have more varied amounts of snow. The hills and mountains of Cumbria and Northumberland could see 10-15cm, whereas the higher parts of Lancashire and Yorkshire closer to 3-8cm.

The hills and mountains of Wales could also see as much as 5-10cm of snow, which combined with strong winds could give blizzards at times.

The rest of the UK will have fewer snow showers – especially the further south and east that you go, meaning that most places will see no more than a light covering of 1-5cm at best.

How much uncertainty is there?

While there is confidence in where the heaviest and most frequent snow showers will fall, there is uncertainty about little areas of low pressure pushing southwards.

These are much smaller than our typical low pressure systems, meaning that weather computer models have difficulty predicting them more than 24-36 hours ahead.

So there is a risk that if one of these little low pressure systems does develop, snow could accumulate in greater amounts of further southwards than initially thought.

You can find out more about why snow is so challenging to forecast in the UK in one of my previous blogs. I’ll also be posting regular updates on Twitter – @liamdutton

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