A blizzard is distinguished by certain conditions:
Temperatures below –7°C (20°F); –12°C (10°F) for a severe blizzard.
Winds greater than 56 kmh (35 mph); 72 kmh (45 mph) for a severe blizzard.
Snow so heavy that visibility is 2/5 km (1/4 mile) or less for at least three hours; near zero visibility for a severe blizzard
Blizzards happen across the middle latitudes and toward the poles, usually as part of a mid-latitude cyclone. Blizzards are most common in winter, when the jet stream has traveled south and a cold, northern air mass comes into contact with a warmer, semitropical air mass
In winter, a continental polar air mass travels down from Canada. As the frigid air travels across one of the Great Lakes, it warms and absorbs moisture.
Blizzards are often part of a mid-latitude cyclone where the jet stream brings cold air into contact with warm moist air.
The difference in pressure between the air masses brings about strong winds.
Cold polar air absorbs moisture as it travels over the Great Lakes and then dumps it as snow downwind to create lake-effect snow.