What Causes a Blizzard?
Heavy snow, bitter cold, whipping winds … Winter storms are no picnic, but what is the official definition of a blizzard, and what causes them, anyway?
The National Weather Service defines a blizzard as any severe snowstorm that is accompanied by strong winds — at least 35 mph — resulting in low visibility. The defining factor of a blizzard is actually the strength of the wind, rather than the amount of snow. To qualify as a blizzard, the combination of wind and snow must reduce visibility to a quarter mile or less and last for at least three hours. Severe blizzards can reduce visibility to zero, making it difficult to see buildings or trees just a few yards away.
While blizzards often feature extreme cold and heavy snow, there are actually no temperature or snow depth requirements for a storm to qualify as a blizzard. Occasionally, blizzard conditions will present when there is no precipitation. The fierce winds pick up existing precipitation on the ground to create what is known as a “ground blizzard.”
Blizzards can be very dangerous. The low visibility can make travel impossible, and some people have even gotten lost walking on their own property. Intense blizzards can result in whiteout conditions, where the horizon completely disappears. In addition, cold temperatures and strong winds can combine to create punishing wind chill factors, resulting in frostbite or hypothermia.
In the United States and Canada, the areas most prone to blizzards are the plains states and provinces, the Great Lakes region, and the Northeastern U.S. and Canadian Maritimes. Blizzards over the plains regions generally form when the jet stream causes cold, dry northern air to collide with warm, humid southern air. In the northeast, blizzards usually come from hurricane force storms moving down from the northern Atlantic Ocean. Because of the direction these storms move in from, they are known as Nor’easters.
The Great Lakes region is especially lucky, because it is positioned to be hit by both types of storms. This region is also subject to heavy lake effect snow and wind, creating even more opportunity for blizzard conditions.