Blizzards occur whenever a winter weather system pairs heavy snowfall with high winds, or when a winter windstorm strikes an area that has recently experienced heavy snowfall. If the storm creates sustained winds of at least 35 miles per hour and reduces visibility to a quarter-mile or less due to blowing snow, it is defined as a blizzard.
Blizzards can form under a variety of meteorological conditions, but any time cold polar air encounters a warm, humid front, the conditions are ripe for heavy snowfall and strong winds. In the same way two conflicting fronts create a thunderstorm during the summer, the temperature difference in the two fronts creates massive updrafts, carrying warm, moist air aloft. The warmth provides energy for the storm system, and the moisture seeds the clouds with ice crystals that will later fall as snow.
Blizzards tend to be most frequent in the Great Plains and New England due to the presence of the northern jet stream. The southern United States rarely gets cold enough for the prolonged snowfall necessary to create a blizzard, although a few exceptions have occurred such as the "perfect storm" of 1993. The Pacific Ocean prevents most blizzards on the West Coast due to its ability to store the sun's energy and moderate temperature swings.