A winter storm is an event in which the dominant varieties of precipitation are forms that only occur at cold temperatures, such as snow or sleet, or a rainstorm where ground temperatures are cold enough to allow ice to form (i.e. freezing rain). In temperate continental climates, these storms are not necessarily restricted to the winter season, but may occur in the late autumn and early spring as well. Very rarely, they may form in summer, though it would have to be an abnormally cold summer, such as the summer of 1816 in the Northeast United States of America. In many locations in the Northern Hemisphere, the most powerful winter storms usually occur in March Fact: date=March 2009 and, in regions where temperatures are cold enough, April.

Snow

A massive snowstorm with strong winds and other conditions meeting certain criteria is known as a blizzard. A large number of heavy snowstorms, some of which were blizzards, occurred in the United States during the early and mid-1990s, and the 1993 "Superstorm" was manifest as a blizzard in most of the affected area.

Large snowstorms could be quite dangerous: a 6 in. (15 cm.) snowstorm will make some unplowed roads impassible, and it is possible for automobiles to get stuck in the snow. Snowstorms exceeding 12 in. (30 cm.) especially in southern or generally warm climates will cave the roofs of some homes and cause the loss of power. Standing dead trees can also be brought down by the weight of the snow, especially if it is wet or very dense. Even a few inches of dry snow can form drifts many feet high under windy conditions.

Snowstorms are usually considered less dangerous than ice storms. However, the snow brings secondary dangers. Mountain snowstorms can produce cornices and avalanches. An additional danger, following a snowy winter, is spring flooding if the snow melts suddenly due to a dramatic rise in air temperature. Deaths can occur from hypothermia, infections brought on by frostbite, car accidents due to slippery roads, fires or carbon monoxide poisoning due to alternative heating methods after a storm causes a power outage, or heart attacks caused by overexertion while shoveling heavy wet snow.

Wintry showers or wintry mixes

Freezing rain storms and ice storms

Main: Ice storm

Heavy showers of freezing rain are one of the most dangerous types of winter storm. They typically occur when a layer of warm air hovers over a region, but the ambient temperature is near 0 °C (32 °F), and the ground temperature is sub-freezing. A storm in which only roads freeze is called a freezing rain storm; one resulting in widespread icing of plants and infrastructure is called ice storm.