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Blizzards and snow drifts

What is a blizzard?

At the Met Office we define a blizzard as moderate or heavy falling snow (either continuous or in the form of frequent showers) with winds speeds of 30 mph or more and a reasonably extensive snow cover reducing visibility to 200 metres or less.

The phrase originated in North America, the term originally referring to a blast of gunfire. In the UK, in common usage the word often refers to any remarkably heavy fall of snow.

How do blizzards occur?

Blizzards can occur either when snow is falling in windy conditions or when it is lifted from the ground by strong winds (known as a 'ground blizzard') or a combination of both facts.

A 'whiteout' is an extreme form of blizzard in which downdrafts and heavy snowfall combine to create a situation in which it is impossible to tell the ground from the sky.

What are snow drifts?

A drift is where snow gets piled up as the wind blows across it. Dry, powder snow is the easiest type of snow to move around because it doesn’t stick together like wet snow. The air temperature and dew point must be below 0°C to give us cold and dry air.

The next ingredient is the wind, which must be at least 10 mph to get the snow on the move. The stronger the wind the more it’s shifted and you can end up with really deep areas of snow piled against road sides, houses or anything that’s facing the wind.

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