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Blizzard is a blinding snowstorm with strong, cold winds. A blizzard occurs when a cold air mass moves out of the Arctic into the Temperate Zone. The advancing heavy, cold air forces the warmer, moist air to rise along the boundary between the two air masses. This boundary is called a cold front. The rising action produces a heavy snowstorm, which is accompanied by cold north winds. Many blizzards follow a period of unusually warm weather in winter.

The National Weather Service of the United States defines a blizzard as a storm with considerable falling or blowing of snow with winds of 35 miles (56 kilometers) per hour or more. The winds are accompanied by temperatures as low as 10 °F (-12 °C) and visibility less than 500 feet (150 meters). A severe blizzard has winds of more than 45 miles (72 kilometers) per hour accompanied by temperatures less than 10 °F and visibility approaching zero.

Blizzards occur most frequently in the northern Great Plains of the United States, in eastern and central Canada, and in various parts of Russia. They may pile up huge snowdrifts that completely disrupt daily life. Sometimes all transportation stops and businesses close down for several days.