Snowsquall
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A Snowsquall is a sudden snow shower with blowing snow due to high winds. It is similar to a blizzard but is localized in time or in space.
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[edit] Types
There are two types of snowsqualls
[edit] Lake effect snow
When arctic air move over large expanses of warmer open waters in winter, convective clouds develop which cause heavy snow showers due to the large amount of moisture available. Whiteout conditions will affect narrow corridors from shores to inland areas aligned along the prevailing wind direction. This will be enhanced when the moving air mass is uplifted by higher elevations. The name originates from the Great Lakes area of North America, however any body of water can produce them. Regions in lee of oceans, such as the Canadian Maritimes could experience such snowsqualls.
The areas affected by lake effect snow are called snowbelts and deposition rate of many inches (centimetres) of snow per hour are common is these situations. In order for lake effect snow to form, the temperature difference between the water and 850 mbar should be at least 13 °C and surface temperature be around the freezing mark. Extremely cold air over still warm water in early winter can even produce thundersnow, snow showers accompanied by lightning and thunder.
[edit] Frontal snowsquall
It is an intense frontal convective line, when temperature is near freezing at the surface. The strong convection that develops has enough moisture to produce whiteout conditions at the passage of the line as the wind cause intense blowing snow. This type of snowsquall last generally less than 30 minutes at any point along its path but the motion of the line can cover large distances.
This is similar to a line of thunderstorms in the summer but the tops of the clouds are only 5 to 10,000 feet, often difficult to see on radar. Forecasting these types of event is equivalent to summer severe weather forecast for squall lines: presence of a sharp frontal trough with wind shift and low level jet of more than 30 knots. However, the cold dome behind the trough is at 850 mbar instead of a higher level and must be at least -25 °C.
[edit] Dangers
Both types of snowsqualls are very dangerous for motorists as the change in conditions is very sudden often producing multiple-vehicle collisions. In the case of lake effect snow, heavy amounts of snow will accumulate, possibly causing road closures and paralyzing cities.
[edit] See also
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[edit] Related articles
Warnings about lake effect snow:
United States
Canada:
