Dear Tom,
I have heard the word “blizzard” used to describe many different kinds of heavy snow. What is the actual definition of a blizzard?
Tom Blaskson, Oak Brook

Dear Tom,
“Blizzard” is a frequently misused weather term, but an actual definition as used by the National Weather Service does exist. Here it is: A blizzard is an intense winter storm with sustained winds of 35 miles per hour or higher and sufficient falling or blowing snow to reduce visibility below one quarter (1/4) mile for three hours or longer. A blizzard is visibility and wind dependent, but the definition does not require that snow actually be falling. Temperature is not part of the definition, though sub-freezing temperatures are surely necessary. Snow, whether it is falling snow or old snow on the ground that has been picked up by the wind and blown into the air, is part of the definition only to the extent that its presence reduces visibility below one quarter mile for at least three hours. It is incorrect to link snow amounts to blizzards. Few of Chicago’s heaviest snowstorms have been accompanied by genuine blizzard conditions.

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