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The Making of a Winter Storm

written by: Dr Mike C•edited by: Donna Cosmato•updated: 9/27/2012

On average, winter storms will kill 41 Americans this year as a result of the extreme cold (exposure) and accidents caused by the weather (mainly car crashes).

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    As the name implies, a winter storm will occur during the winter seasons in both the Northern and Southern hemispheres, but outside of the Tropics, of course. They can be severe weather events and be associated with extreme cold; heavy snowfall and blizzard conditions; and severe flooding. On average, winter storms claim the lives of 41 Americans each season. The Federal Emergency Management Agency has some advice on their website on what to do if you are threatened by a winter storm, or have the misfortune to be caught out in one [1].

    Aircraft encountering the cold air associated with a winter storm might suffer from icing on flight surfaces, if the aircraft is not designed, or treated, for such an eventuality.

    Icing was believed to be responsible for up to 30 air accidents a year, on average, between 1975 and 1988 in the USA. This serves to highlight the importance of accurate weather forecasting, particularly for private civil aviation.

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    Defining A Winter Storm

    According to the National Weather Service in Buffalo, New York, a winter snow storm for this part of the U.S. is any storm which drops more than seven inches (17.5 cm) of snow within a 24 hour period – but that is a moveable feast! In the UK, any snowstorm that drops more than a couple of inches of snow will paralyze the rail transport system and leave roads in a treacherous condition. On the other side of the English Channel, particularly in Alpine regions, the locals would not miss a beat.

    The necessary ingredients for a winter storm are moisture, cold air and lift (i.e. a mechanism to get the moisture to altitude).

    The air at altitude (or ground level) needs to be below 0 °C for snow to form and it has to be laden with moisture. Air masses can pick up moisture as they cross large bodies of water such as the ocean or large inland lakes. The element of lift can be provided in various ways. These include air flow up the side of a mountain; the interaction of cold and warm fronts as warm air passes over the cold air mass; and upper atmospheric level pressure troughs (depressions). Well, that answers the question of what is a winter storm, but it doesn’t fully address the types of weather that can be associated with one.

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    Weather Events Associated With These Storms

    If the temperature near to the ground level is below freezing, and the overlying cloud base generates rain, an ice storm can be formed as the rain is turned to ice as it moves through colder air near to the surface. Ice storms can be significant weather events, bringing down power lines and trees because of the weight of ice that is deposited on these structures and wind associated with the storm.

    The winds that can be associated with a winter storm may cause blizzards if the storm generates snow fall. The wind can drive the snow into 'whiteouts', dropping visibility to next to zero, and causing the drifting of lying snow to occur. This can cause significant deposits of snow to accumulate in some regions, while other areas may be almost blown free of snow. Driving is extremely dangerous because of the impaired visibility and the loss of grip on the road due to ice/slush/snow mixtures.

    A winter storm can be accompanied or followed by extremely cold weather, which can be dangerous due to the cold and the fact that wind chill can worsen the effects of the cold, increasing the risk of hypothermia to people caught outside during the storm.

    In some instances, a winter storm may also be associated with a thunder storm, depending on just how the storm forms, but this is not a common feature.

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    References

    1. FEMA, Winter Storms: http://www.ready.gov/winter-weather
    2. National Weather Service: http://www.wbuf.noaa.gov/wint97ny.htm
    3. MetEd Universities Corporation for Atmospheric Research: http://www.meted.ucar.edu/hazwx/topic3/fact9.htm