Freezing rain warning for Scotland

Freezing rain
Image caption Supercooled water droplets freeze instantly when they hit cold surfaces

A severe weather warning has been issued for much of Scotland as a band of freezing rain passes over the country later.

The Met Office said an area of rain would move south-eastwards across Scotland, affecting most areas apart from the far north and west.

Forecasters are predicting the rain will freeze instantly as it hits very cold surfaces in some places.

The resulting ice could make pavements and roads "extremely hazardous".

A weather warning on the Met Office site said the warning level could be upgraded from yellow to amber later as there was some uncertainty about how severe the ice problems would be.

Freezing rain occurs when droplets fall through air with a temperature below zero. They then freeze on impact with the ground, forming a clear ice known as a "glaze".

Supercooled droplets

Transport Minister Keith Brown said: "With these Met Office yellow warnings in place, it is important that people travelling on the roads take extra precautions and check travel bulletins or the Traffic Scotland website for the latest advice.

"The public should be aware that pavements could be very dangerous locally, and driving conditions could become extremely hazardous, particularly as freezing rain is so difficult to treat.

"Transport Scotland, its operating companies and the Met Office have been in regular contact to monitor conditions as they arise and to deploy front line patrol, gritters and support vehicles this evening and into tomorrow.

"As a precaution, we will be activating some of the Multi Agency Response Team partners from 5am tomorrow to coordinate our response to the conditions."

A post on the Met Office blog said: "Conditions have to be 'just right' to get freezing rain and it doesn't happen very often in the UK, making it a relatively rare phenomenon.

"Generally, freezing rain starts its life as snow, ice, sleet or hail, but passes through a layer of warmer air on the way down. This causes it to melt and return to a liquid form.

"As it continues towards the ground, it then briefly passes through colder air again, causing the water droplets to become 'supercooled' - colder than 0C but still in liquid form."

As the "supercooled" droplets freeze on the ground they can quickly create "treacherous conditions".

The Met Office said the droplets became "supercooled" rather than frozen as water needed small particles of dust or dirt to freeze around.

Without the particles, water can remain in liquid form well below freezing.

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