Blizzards
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| Photo: NWS-Flagstaff |
What is a blizzard?
Blizzards are dangerous winter storms that are a combination of blowing snow and wind
resulting in very low visibilities. While heavy snowfalls and severe cold often accompany
blizzards, they are not required. Sometimes strong winds pick up snow that has already
fallen, creating a ground blizzard.
Officially, the National Weather Service defines a blizzard as a storm which contains
large amounts of snow OR blowing snow, with winds in excess of 35 mph and visibilities of
less than 1/4 mile for an extended period of time (at least 3 hours). When these conditions
are expected, the National Weather Service will issue a "Blizzard Warning". When these
conditions are not expected to occur simultaneously, but one or two of these conditions
are expected, a "Winter Storm Warning" or "Heavy Snow Warning" may be issued.
Blizzard conditions often develop on the northwest side of an intense storm system. The
difference between the lower pressure in the storm and the higher pressure to the west
creates a tight pressure gradient, or difference in pressure between two locations, which
in turn results in very strong winds. These strong winds pick up available snow from the
ground, or blow any snow which is falling, creating very low visibilities and the potential
for significant drifting of snow.
Where did the term blizzard come from?
In the 1870's, an Iowa newspaper used the word "blizzard" to describe a snowstorm.
Previously, the term blizzard referred to a canon shot or a volley of musket fire. By the
1880's, the use of the word blizzard was used by many across the United States and in
England.
The upper Midwest and Great Plains of the United States tends to be the region that
experiences blizzards most often. With few trees or other obstructions to reduce wind and
blowing snow, this part of the country is particular vulnerable to blizzards. However,
blizzards can occur in any location that has a climate that experiences snowfall. Northern
Arizona can experience blizzard conditions when a strong low pressure system moves across
southern Arizona and high pressure builds strongly into the Great Basin. However, these
conditions are rarely met due to the infrequency of strong low pressure systems moving
through the state.
What makes a blizzard dangerous?
Blizzards can create life-threatening conditions. Traveling by automobile can become
difficult or even impossible due to "whiteout" conditions and drifting snow. Whiteout
conditions occur most often with major storms that produce a drier, more powdery snow. In
this situation, it doesn't even need to be snowing to produce whiteout conditions, as the
snow which is already on the ground is blown around, reducing the visibility to near zero
at times.
The strong winds and cold temperatures accompanying blizzards can combine to create
another danger. The wind chill factor is the amount of cooling one "feels" due to the
combination of wind and temperature. During blizzards, with the combination of cold
temperatures and strong winds, very low wind chill values can occur. It is not uncommon in
the Midwest to have wind chills below -60F during blizzard conditions. Exposure to such low
wind chill values can result in frostbite or hypothermia. For more information, go to the NWS
wind chill web page.
Blizzards also can cause a variety of other problems. Power outages can occur due to
strong winds and heavy snow. Pipes can freeze and regular fuel sources may be cut off.
Winter Weather Safety
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| Photo: NOAA |
People should never venture out in blizzards, nor should they continue to travel if a
storm is upgraded to a blizzard. To protect yourself from the effects of winter storms,
including blizzards, the National Weather Service suggests the following web resources:
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www.weather.gov 
