Freezing rain is due to fall over the weekend across the UK and is predicted to cause significant disruption.
The Met Office has issued yellow and amber weather warnings for most of the country on Saturday and Sunday.
The icy weather is likely to bring power cuts, cause vehicles to be stranded on roads, and could lead to delays and cancellations at train stations and airports.
What is freezing rain?
Freezing rain is a rare form of precipitation that freezes almost instantly after striking a cold surface, giving everything from leaves to car mirrors the appearance of ice sculptures.
These scenes may be pretty, but they can be dangerous. The weight of the ice brought about by freezing rain can be heavy enough to bring down power lines and fell trees; the instant freezing effect is a big problem for gritters as the rain can instantly coat roads and runways in slippery ice.
Freezing rain is more common in the US and other parts of the world, which are more prone to experiencing ice storms as a result.
What causes freezing rain?
Rain often begins as snow, hail or sleet when the air is cold enough. As it falls, it may pass through warmer air, and melt into rain droplets before cascading off your umbrella.
Freezing rain occurs when the droplets instead pass through another layer of cold air before landing. The droplets become “supercooled”, meaning they are still falling in liquid form even though their temperature has fallen below freezing.
When these supercooled droplets hit surfaces on the ground that are also below zero, they spread a little before instantly glazing with ice whatever they have made contact with.
How is rain supercooled?
Raindrops form around microscopic particles of dust or dirt, also known as cloud condensation nuclei. The droplets can only freeze if they have an ice nucleus, but it is possible for them to exist several degrees below freezing and hold their liquid form without a nucleus. This is when they are supercooled.
