Snowstorms are storms where large amounts of snow fall. Snow is less dense than liquid water, by a factor of approximately 10 at temperatures slightly below freezing, and even more at much colder temperatures. Therefore, an amount of water that would produce 0.8 in. (2 cm.) of rain could produce at least 8 in (20 cm) of snow. Two inches of snow (5 cm.) is enough to create serious disruptions to traffic and school transport (because of the difficulty to drive and maneuver the school buses on slick roads). This is particularly true in places where snowfall is uncommon but heavy accumulating snowfalls can happen (e.g., Dallas, Atlanta, Seattle, London, Dublin, Canberra, Vancouver and Las Vegas). In places where snowfall is common, such as Utica, Detroit, Denver, Ottawa, Montreal, Quebec City, Chicago, Syracuse, Buffalo, Columbus, Pittsburgh, Toronto and Minneapolis, such small snowfalls are rarely disruptive, because of effective snow and ice removal by municipalities, greater usage of snow tires and drivers more used to winter conditions. Snowfalls in excess of 6 in (15 cm) are usually universally disruptive.

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 1888 and 1947 as well as the early and mid-1990s. The snowfall of 1947 exceeded two feet with drifts and snow piles from plowing that reached twelve feet and for months, temperatures did not rise high enough to melt the snow. 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 impassable, 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.

Dangers of Snow

Snowstorms are usually considered less dangerous than ice storms. However, the snow can bring 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 or car accidents due to slippery roads. Fires and carbon monoxide poisoning can occur after a storm causes a power outage. Large amounts of snow can also significantly reduce visibility in the area, a phenomenon known as a whiteout; this can be very dangerous to those who are in a densely populated area, as the whiteout can cause major accidents on the road or while flying. There is also several cases of heart attacks caused by overexertion while shoveling heavy wet snow. It is difficult to predict what form this precipitation will take, and it may alternate between rain and snow. Therefore, weather forecasters just predict a "wintry mix". Usually, this type of precipitation occurs at temperatures between -2 °C and 2 °C (27 °F and 36 °F).

A blizzard is a severe snowstorm or winter storms characterized by low temperature, strong winds, and heavy snow. The difference between a blizzard and a snow storm is the strength of the wind. To be a considered a blizzard, the storm must have winds in excess of 35 miles per hour, it should reduce the visibility to 1/4 miles, and must last for a prolonged period of 3 hours or more. Ground blizzards require high winds to stir up snow that has already fallen, rather than fresh snowfall. Blizzards have a negative impact on local economics and can terminate the visibility in regions where snowfall is rare.

Blizzards can bring near-whiteout conditions, and can paralyze regions for days at a time, particularly where snowfall is unusual or rare. The 1972 Iran blizzard, which caused approximately 4000 deaths, was the deadliest in recorded history.

List of Blizzard Events

• Ground Hog Day Blizzard of 2011
• The New York blizzard in 2010
• Third North American blizzard of 2010
• Second North American blizzard of 2010
• First North American blizzard of 2010
• February 2007 North America Winter Storm
• Saskatchewan blizzard of 2007
• Blizzard of 1999
• Great Blizzard of 1993
• Halloween Blizzard of 1991
• Chicago Blizzard of 1979
• Northeastern United States Blizzard of 1978
• Great Blizzard of 1978
• Blizzard of 1977
• Chicago Blizzard of 1967
• North American blizzard of 1947
• Armistice Day Blizzard of 1940
• Great Lakes Storm of 1913
• Schoolhouse Blizzard of 1888, North American Great Plains
• Great Blizzard of 1888, Northeastern U.S.