Winter storms vary in size and strength and can be accompanied by strong winds that create blizzard conditions and dangerous wind chill. There are three categories of severe winter storms. A blizzard is the most dangerous of all winter storms. It combines low temperatures, heavy snowfall, and winds of at least 35 miles per hour, reducing visibility to only a few yards. A heavy snowstorm is one that drops 4 or more inches of snow in a 12-hour period. An ice storm occurs when moisture falls and freezes immediately upon impact.