Frost pockets and frost hollows

Simple explanation

Issued 09/04/2015

Sometimes in the weather forecast you’ll see the term frost pocket (or frost hollow) being used. What does it refer to?

Very simply frost pockets are places where frost is more likely to form. They are usually found in valleys because on calm and clear nights the air near the surface cools. Cooler air is denser and sinks, causing it to flow down into valleys and become trapped making frost more likely to form than on the surrounding hills.

The flow of the colder and denser air into the valley is caused by gravity and is called a Katabatic wind. Katabatikos is the Greek word meaning "to flow downhill".

By allen watkin from London, UK (Frosty) [CC BY-SA 2.0], via Wikimedia Commons

Frost pockets are found across the UK but care particularly common in the Scottish glens and parts of Wales. In England famous frost pockets include Benson in South Oxfordshire and Rickmansworth in Hertfordshire.

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