Ding, ding… Mild air versus cold air round two

At the weekend, the weather is set to reach another interesting fork in the road. Mild air that was forced out of the way by cold air last weekend will try to make a return across the UK.

In the process of doing so, where the mild, moisture laden air meets the cold air, there is a chance of seeing some notable snowfall.

Once again, however, there is a lot of uncertainty as to how quickly this will happen, how much snow there will be and where it is most likely.

The difficulty with weather computer models is that they are often too eager to push cold air out of the way. Cold air is dense and digs in at the surface, making it reluctant to move very quickly.

When mild air moves in, it rises over this wedge of dense, cold air and, for a while at least, snow falls before eventually turning back to rain.

The additional problem that can result is freezing rain, which happens when the ground temperature is still at freezing or below and rain falls on it, freezing upon impact.

Widespread freezing rain situations are not that common in the UK, but when they do occur can be extremely disruptive with everything ending up coated in a layer of ice.

So what are the latest weather computer models saying? Well there is quite a spread of possible outcomes.

One of the weather computer models called the GFS (Global Forecast System) which is run by NOAA in the US is not keen on that much snow here in the UK.  

It predicts a band of snow moving in during Saturday night, with most places having a few centimetres. However, it quickly turns it back to rain with a thaw setting in on Sunday as milder air floods in from the west.

Another weather computer model called the ECMWF (European Centre for Medium-Range Weather Forecasts) is keen to produce a lot more snow, predicting that most places could see 5-10cm, locally more by the end of Sunday.

It is also in favour of the cold air hanging on for longer, hence why it is keen to predict more snow.

So at this stage the weekend could potentially bring a spell of snow, but it is worth emphasising that it is still four days away and a lot can change between now and then.

I’ll of course keep you updated here on my blog, as well as posting mini updates on Twitter – @liamdutton

There’s also the website channel4.com/weather and my forecast on TV each weekday evening after Channel 4 News.