Blowing snow during a blizzard reduces visibility.
Credit: NOAA National Weather Service images by Ben Jacquot

Snow whirling around in wind blowing faster than highway speed limits makes the whole world look white. Imagine snow so deep that second graders can’t see over the top of it. The wind and the snow may cause a power outage and collapse roofs. That’s what you can expect from a blizzard.

The National Weather Service defines a blizzard as a storm with large amounts of snow or blowing snow, winds greater than 35 mph (56 kph), and visibility of less than ¼ mile (0.4 km) for at least three hours. Some blizzards, called ground blizzards, have no falling snow. Instead, snow that had fallen before the blizzard is blown around or drifts in a way to create these conditions.

Conditions for a blizzard usually will build up on the northwest side of a powerful storm system. The storm produces ample snow while strong winds develop because of a difference in pressure between the low pressure of the storm and the high pressure beyond the storm.

In the United States, blizzards are common in the upper Midwest and the Great Plains but occur in most areas of the country except for the Gulf Coast and the California coast. Blizzards can occur all over the world, even in the tropics where it is cold on high altitude mountaintops.

Conditions of a blizzard can be severe. Travel becomes dangerous when the blowing snow causes whiteout conditions and sky and ground look white. Roads can be partially or fully blocked by snowdrifts – piles of snow formed by the wind. Many times cold temperatures that can cause frostbite or hypothermia are part of a blizzard and can last for days after the storm has ended.

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