Icy beauty - The science behind rime ice

Once winter's chill settles in, rime ice can form due to low clouds or fog, especially in high elevations. All you need are surface temperatures below freezing. So how does it work?

Rime ice is a type of frozen precipitation that forms when supercooled liquid droplets freeze onto surfaces. The droplets usually come from fog or low-lying clouds, and they freeze instantly upon contact with a surface that is at or below freezing temperature. Have you seen any freezing temperatures on our TemperatureRadar?

When the ice forms, it can look fuzzy or feathery, just like it did in Italy's Ligurian Apennines on Monte Reixa in mid-December 2024. Closer to home, Mount Washington in New Hampshire often sees this weather phenomenon due to the mountain's elevation of over 6,000 feet and, therefore, very cold temperatures at the mountaintop.

The feathery, fuzzy texture of rime ice is caused by the way the supercooled droplets freeze. As the droplets freeze, they release heat, which causes the surrounding air to expand rapidly. This expansion causes the droplets to break apart and form a mist, which then freezes to form feathery crystals of rime ice.

You can look for the wintertime fog or low clouds on the WeatherRadar. They show up rather thick on the satellite and can often be a problem for air travel when the aircraft surface is at or below freezing. Remember the last time you had to wait for the air traffic crew to de-ice the plane? Now you know part of why they're taking these precautions!