What is Freezing rain and why is it one of winters most dangerous hazards?

Freezing rain on a car Photo: iStock

It's a winter hazard that is rare for the United Kingdom, but when it arrives it can cause severe disruption, but what actually is it?

Freezing Rain in brief:

  • Freezing rain occurs when the atmosphere is too warm for snow, but the ground is below zero
  • It can lead to major tree damage and widespread power cuts
  • It produces a glaze of ice to surfaces it comes in contact with leading to black ice on roads
How freezing rain forms Credit: Weather Channel

How does Freezing Rain form?

Freezing rain starts its life as snow, sleet or hail where the atmosphere is below freezing, but as it falls to the earth it passes through a layer of air that is above 0°C. This melts the ice, turning it back to a liquid water droplet.

If the raindrop falls through a zone of air that is below zero, located just above the ground it becomes supercooled. This is where water can be in its liquid state at a temperature below zero.....incredible isn't it! The reason this happens is because the water droplet doesn't have a nucleus (what we call in meteorology as "condensation nuclei") for it to freeze around.

Supercooled water is where water is at a temperatures below freezing but remains in its liquid state

– Chris Page, Meteorologist
Freezing rain on branch Credit: Met Office

As the supercooled water droplets come into contact with a surface that is close to or below freezing it instantly freezes, forming glaze ice.

This can build up to be several centimeters thick, which can have the ability to break tree branches and pull down power lines.

Why is it rare in the UK?

Although it's more common in the United States, it's rare in the UK as it requires very specific conditions. We are more likely to see rainfall onto frozen surfaces freezing as the temperatures drop below zero.

Freezing rain leaving an ice glaze Credit: Alex Burkill

Why is it so dangerous?

  • The invisible killer - it can form black ice on roads, which is near impossible for divers to see.
  • It has the ability to pull down trees and power lines due to the shear weight that builds up as the ice freezes
  • Unlike snow, it cannot be ploughed and it doesn't run off like rain which makes getting rid of it difficult

WATCH our Meteorologist Chris Page explain what Freezing Rain is here

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