Chicago winter storm: What's the difference between a snowstorm and blizzard?
CHICAGO (CBS) -- What's the difference between a snowstorm and a blizzard? How does a snowstorm become a blizzard?
If you think it's just about how much snow falls, think again. While snow is obviously an important factor, it's also about wind and visibility.
A blizzard is a snowstorm with strong, sustained winds and poor visibility. To qualify as a blizzard, a storm must have large amounts of snow or blowing snow, sustained or frequent winds stronger than 35 mph, and visibility of less than ¼ mile for at least three hours.
It's possible to have a blizzard without falling snow if the snow already on the ground is blown around or drifts long enough to create blizzard conditions.
The forecast for Friday's winter storm has the potential for blizzard conditions, with heavy snow and strong winds throughout the day. Areas west of Chicago and near the Wisconsin border could see 6 to 12 inches of snow and severe storm impacts.
Areas south of the city can expect several inches of snow. Wind gusts up to 45 mph are possible.
The National Weather Service has not issued a blizzard warning for the Chicago area as of Friday morning. A winter storm warning is in effect for most of the Chicago area through noon Saturday.
The worst blizzard to hit Chicago happened in January 1967 when nearly two feet of snow fell, and winds howled up to 50 mph, creating drifts as high as 10 feet.