What are rainbow clouds and why do they happen? Weather watchers spot nacreous clouds across UK

A colourful, nacreous cloud spotted at Bradwell in Norfolk. Picture: Owen Curtis
A beautiful and rare nacreous cloud spotted in Bradwell, Norfolk Credit: Owen Curtis

Colourful "rainbow clouds" have been spotted in the sky across the UK, leading hundreds of people to post social media pictures of the stunning iridescent displays.

The phenomenon - called nacreous clouds in meteorological terms - show clouds take on a "mother-of-pearl" appearance and is a rare sight in the UK.

But what causes them?

These are an extremely rare sight in Britain - you can only ever see them at sunrise or sunset in the wintertime when the sun is low in the sky or below the horizon.

They occur at about 70,000 to 100,000 feet above the earth's surface. That's above where our everyday weather occurs in an area called the stratosphere.

Nacareous Clouds in Snettisham, Norfolk Credit: Nicky Burdett

The clouds are made of minute ice crystals which act like prisms refracting and reflecting the sunlight from below to produce what is known as cloud iridescence.

This gives them an oil-like appearance in the sky which ultimately produces these gorgeous, beautiful colours like we have seen today."

The weather anomaly is a winter phenomenon occurring only when exceptionally cold air is pushed southwards from the Arctic.

The clouds have been visible in many parts of the country on Thursday due to a storm system which has affected parts of Norway and Denmark and which brought strong winds to UK shores.

Nacreous clouds in Gorleston Credit: Jimmy Flaxman
Nacreous Clouds captured in Westleton Suffolk Credit: Karen Dutton
Rare Nacreous clouds in Peterborough Credit: Neil Pettitt

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