What is freezing rain?

During last week’s cold spell, there was a real mixture of wintry hazards across the UK, with some places having freezing rain, yet other places relatively close by having snow.

Having asked on Twitter which weather related topics you would like explained, the issue of freezing rain seemed to be the most popular request, so here goes…

You probably think that as you go higher up in the atmosphere, the temperature decreases. In most cases this is true, but there are occasions when the temperature can actually stay the same or even rise at certain points in the atmosphere.

In a situation where snow falls, the temperature at the base of the cloud from which flakes fall could be, for example, around -15C. As long as the temperature between the base of the cloud and the ground remains around freezing, then the snowflakes reach the ground in tact.

It’s a similar situation for sleet, although the temperature near the surface of the ground may be around 1-4C, which causes some of the snow flakes to melt, which is why a mixture of rain and snow occurs.

However, if sleet falls for some time, the air can actually be chilled by evaporative cooling and as the temperature drops, it can turn from sleet to snow.

There can also be situations where precipitation can change from rain to snow – again, normally when the air temperature is in the range of 1-4C.

Freezing rain is a little more complicated in that a layer of warm air rises over a layer of cold air at the surface. This effectively forms a sandwich of air at different temperatures – imagine each piece of bread as the cold air, with the warm air providing the filling.

So for example, the air at the base of the clouds from which snow flakes fall could be -15C. There then lies a layer of warmer air with a temperature a few degrees above freezing, which melts the snow flakes into liquid form – rain drops.

These rain drops then fall further and encounter the wedge of very cold air at the surface which is at or below freezing, become cooled very quickly and freeze upon hitting frozen ground, giving freezing rain.

Such situations can be extremely dangerous as everything becomes coated in a layer of glazed ice very quickly. Effectively, the ground turns into a big ice rink, which remains in place until the temperature of the air and ground rises sufficiently above freezing to melt the ice.

This happened in northern parts of England at the end of last week, causing numerous accidents on the roads. The picture above from Kasim Awan shows freezing rain that fell on the bonnet of a car in Manchester, giving a thick layer of ice.

Thankfully freezing rain doesn’t occur in the UK that often and with a mild week ahead, there are no signs of any wintry hazards to watch out for during the next few days.

If there’s anything weather related that you’d like me to explain, then feel free to contact me on Twitter – @liamdutton