Storm Deirdre: What is freezing rain and how common is it in the UK?

Credit: Met Office
Credit: Met Office
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Freezing rain can quickly glaze an area with ice and leave roads and pavements in a dangerous condition, but fortunately it is relatively rare in the British Isles.

What is freezing rain?

According to the Met Office, freezing rain occurs when rain falls through sub-zero temperature air to become supercooled water that freezes "almost instantly" when it hits a cold surface.

Supercooled water droplets can exist in a liquid state below zero degrees, and occur in clouds in winter time.

Freezing rain typically starts life as snow, ice, sleet or hail which falls through a layer of air above zero degrees and melts into liquid water.

If these water droplets then pass through a zone of sub-zero air just above the ground, they become supercooled.

When supercooled droplets eventually strike cold ground they freeze on impact, creating a glaze of ice.

Why is it dangerous?

An abundance of freezing rain is called an ice storm and can bring large-scale disruption, the Met Office says.

Ice glaze can collect on trees or power lines which then break from the weight of the build-up.

Motorists and pedestrians are also risk as a glaze can make roads and pavements very slippery.

How common is it in the UK?

The Met Office explains that in some weather systems, for example in parts of the US, freezing rain is common.

But it adds: "The conditions needed for freezing rain to occur are quite specific and we don't see them very often, making this phenomenon quite rare in the UK.

"We are more likely to see rain falling on to already frozen surfaces, or wet surfaces that freeze as temperatures drop below 0C overnight."