A winter storm is an event in which varieties of precipitation are formed that only occur at low temperatures, such as snow or sleet, or a rainstorm where ground temperatures are low 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 Northeastern United States.
1.1 Dangers of snow
2 Freezing rain
Snow Main article: Snow
Chicago's Fullerton Harbor looking south during the January 31 – February 2, 2011 North American winter storm (left) and on a clear day for comparison
Approaching winter storm in Salt Lake City.
Snowstorms are storms where large amounts of snow fall. Two inches
(5 cm) of snow 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 not typical but heavy accumulating snowfalls can
occur. In places where snowfall is typical, such small snowfalls are
rarely disruptive, because of effective snow and ice removal by
municipalities, increased use of four-wheel drive and snow tires, and
drivers being more used to winter conditions. Snowfalls in excess of 6
inches (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 2 feet (61 cm) with drifts and snow
piles from plowing that reached 12 feet (3.7 m) and for months,
temperatures did not rise high enough to melt the snow. The 1993
"Superstorm" manifested as a blizzard in most of the affected areas.
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
electricity. 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
Dangers of snow
Accumulating snow can make driving motor vehicles very hazardous.
Accumulation of snow on roadways reduces friction between tires and
the pavement, which in turn lowers the maneuverability of a vehicle
considerably. As a result, average driving speeds on public roads and
highways are reduced by up to 40% while heavy snow is falling.
Visibilities are reduced by falling snow, and this is further
exacerbated by strong winds which are commonly associated with winter
storms producing heavy snowfall. In extreme cases, this may lead to
prolonged whiteout conditions in which visibilities are reduced to
only a few feet due to falling or blowing snow. These hazards can
manifest even after snowfall has ended when strong winds are present,
as these winds will pick up and transport fallen snow back onto
roadways and reduce visibilities in the process. This can even result
in blizzard conditions if winds are strong enough. Heavy snowfall
can immobilize a vehicle entirely, which may be deadly depending on
how long it takes rescue crews to arrive. The clogging of a vehicle's
tailpipe by snow may lead to carbon monoxide buildup inside the
Depending on the temperature profile in the atmosphere, snow can be
either wet or dry. Dry snow, being lighter, is transported by wind
more easily and accumulates more efficiently. Wet snow is heavier due
to the increased water content. Significant accumulations of heavy wet
snow can cause roof damage. It also requires considerably more energy
to move and this can create health problems while shoveling when
combined with the harsh weather conditions. Numerous deaths as a
result of heart attacks can be attributed to snow removal.
Accretion of wet snow to elevated surfaces occurs when snow is
"sticky" enough which can cause extensive tree and power line damage
in a manner similar to ice accretion during ice storms. Power can be
lost for days during a major winter storm, and this usually means the
loss of heating inside buildings. Other than the obvious risk of
hypothermia due to cold exposure, another deadly element associated
with snowstorms is carbon monoxide poisoning which can happen anytime
combustion products from generators or heating appliances are not
properly vented. Finally, partially or fully melted snow on roadways
can refreeze when temperatures fall, creating black ice.
A sudden rise in air temperature is can result in the rapid melting of
snow. This can create flooding issues if the snowpack has sufficient
water content, and this can be significantly exacerbated by heavy
rainfall and by ice jams which may have formed on area rivers during
prolonged subfreezing temperatures. The re-freezing of previously
melted snow creates potholes in roadways. This process is
accelerated when water is melted and re-frozen multiple times.
Coated in ice, power and telephone lines sag and often break, resulting in power outages.
Plants wrapped in 6 mm (0.24 in) of ice. Severe ice storms, which may occur in the spring, can kill plant life.
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 a few meters above the
ground is near or below 0 °C (32 °F), and the ground
temperature is sub-freezing.
While a 10 cm (3.9 in) snowstorm is somewhat manageable by
the standards of the northern
Comprehensive discussion of weather-related terms, such as Winter
Wikivoyage has a travel guide for Travelling in cold weather.
^ Smith A.B. and R. Katz, 2013: U.S. Billion-dollar