A blizzard is defined as a snowstorm in which air temperatures are low (generally less than -10°C) and winds of at least 30 knots (55.6 km/hr) blow falling snow or that, which has already fallen, such that visibility does not exceed 200 m. It lasts for a prolonged period of time typically three hours or more.
It results from interrelationships among snowfall, temperature, wind and patterns of human activity.
These winds combine with snow and blowing snow to produce extreme conditions.
The difference between a blizzard and a snowstorm is the strength of the wind, not the amount of snow.
While severe cold and large amounts of drifting snow may accompany blizzards, they are not required.
Blizzard conditions of cold temperatures and strong winds can cause wind chill values that can result in hypothermia or frostbite. The wind chill factor is the amount of cooling the human body feels due to the combination of wind and temperature.
There are a number of types of blizzards, each uniquely different from the others.
• A "traditional" blizzard is, for all intents and purposes, a snowstorm. This means that a blizzard will often include heavy snow and below-freezing temperatures. What makes a blizzard different than a snowstorm is that, unlike snowstorms, a blizzard must have high winds of at least 35mph, or 56 km/h. Additionally, a blizzard must reduce visibility to no more than 1,300 feet for extended periods of time.
• Ground blizzards are different from traditional blizzards in that they do not dump any kind of significant snowfall. Instead a ground blizzard occurs when high winds blow snow that has already fallen. There are three main types of ground blizzards: horizontal advection, which has wind blowing horizontally across the Earth's surface, picking up snow and blowing it; vertical advection, in which there is an upward draft with the wind, blowing the snow high into the atmosphere to create waves hundreds of feet in height; and thermal-mechanical, which is essentially a combination of the previous two. While the latter is rare, it can bury a two-story house and be seen from space.
• Lake-effect blizzards, seen most commonly along the shorelines of larger lakes such as the Great Lakes Region of North America, are the products of lake-effect snow combined with high winds. Lake-effect blizzards are relatively rare due to how lake-effect snow is formed. When cold winter winds blow across the warmer lake water, the winds lift the water vapor into the air and this is dumped along the shoreline. Because lake-effect snow doesn't often rise when the winds blow too fast, lake-effect blizzards are rare events.