Shane Brown, age 12, of Oldham, S.D., for his question:

WHAT CAUSES A BLIZZARD?

When a cold air mass moves out of the Arctic area into the Temperate Zone, a blinding snowstorm with strong, cold winds called a blizzard may result. The advancing cold, heavy air forces the moist, warmer air to rise along the boundary between the two air masses. This is called a cold front.

The rising action of a cold front produces a heavy snowstorm, which is accompanied by cold north winds. Many blizzards follow a period of unusually warm weather in winter.

A blizzard is defined as a snowstorm with winds of 35 miles per hour or more and temperatures as low as 10 degrees Fahrenheit. Visibility must be less than 500 feet. A severe blizzard has winds of more than 45 miles per hour, temperatures below 10 degrees and visibility zero.