The National Weather Service defines a blizzard as a winter storm in which two conditions must prevail for a minimum of three hours:
Sustained wind or frequent gusts of 35 miles per hour or greater; and
Visibility of less than one-quarter of a mile
The definition does not include any threshold for the amount of snow produced by the storm.
Before it came to be employed in the context of weather, the term originally was used to describe a cannon shot or a volley of musket fire, the National Weather Service says on its website. It was only in the 1870’s that an Iowa newspaper used the term to describe a snowstorm. By the following decade, the term came into regular usage in the United States and England.
Because of the cold and the low-visibility caused by the blowing snow, blizzards are considered dangerous weather events. Throughout history there have been several severe blizzards that caused damage and loss of life. The deadliest in recorded history was the Iran blizzard of 1972, in which approximately 4,000 people died.