A snowstorm occurs when snow falls as precipitation. The most severe kind of snowstorm is a blizzard, where low temperature, heavy blowing snow, and strong winds combine to create huge piles of snow (snowdrifts) and to create a zero visibility condition that can potentially harm people.

What is a blizzard?

According to the US National Weather Service, a blizzard is a turbulent, freezing snowstorm with a windchill factor of about -20 degrees Fahrenheit (-29 degrees Celsius) or lower and gusty, piercing winds of at least 56 km/h (35 mph). This condition leads to blowing snow, causing visibilities around 400-500 feet. A blizzard usually lasts for at least 3 hours.

In Canada, a blizzard is defined as sustained wind with 25 mph (40 km/h) or more speed, has snow or blowing snow, a windchill factor of -13 degrees Fahrenheit (-25 degrees Celsius) or less, and a 1 km (5/8 mile) visibility. These conditions must last at least 4 hours before the snowstorm can be called a blizzard.

What is a ground blizzard?

A ground blizzard occurs when the above conditions are met but without snow falling. In this type of blizzard, high winds blow all the snow already present at the earth's surface. A perfect condition for a ground blizzard is a large expanse of relatively flat and open land with a plenty amount of accumulated powdery snow (loosely packed) simply being blown around by high winds.

What is a whiteout?

Whiteouts occur when there is so much snow that it is difficult to distinguish the earth from the sky, with the horizon disappearing into a white nothingness. Neither landmarks, nearby objects, clouds, nor shadows are discernible.

As a result, many animals and humans lose their depth perception, sense of direction, and balance. A whiteout can trick travelers and pilots into believing that far is near and thinking down is up. In this disoriented state, many of them freeze to death.

What are the physical and economic threats of blizzards?

Blizzards can have serious effects on health. A blizzard carries the risk of people and animals getting frost bite and hypothermia. It also runs the risk of suffocation and people being stranded. Arctic conditions, 100 mph winds, and extreme temperatures in mountainous regions are additional threats. Blizzards also disrupt local economies. Traffic and commerce are interrupted for days or even weeks, especially in areas where snow removal machines are not available.