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Snowsquall


A snowsquall (or snow squall) is a sudden moderately heavy snow fall with blowing snow and strong, gusty surface winds. It is often referred to as a whiteout and is similar to a blizzard but is localized in time or in location and snow accumulations may or may not be significant.

There are two primary types of snowsqualls, lake effect and frontal.

When arctic air moves 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. This occurs southwest of extratropical cyclones, with the curved cyclonic wind flow bringing cold air across the relatively warm Great Lakes which then leads to narrow lake-effect snow bands that can produce significant localized snowfall.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 in these situations. In order for lake-effect snow to form, the temperature difference between the water and 850 mbar should be at least 23 °F (13 °C), surface temperature be around the freezing mark, the lake unfrozen, the path over the lake at least 100 km, and the directional wind shear with height should be less than 30° from the surface to 850 millibars. Extremely cold air over still warm water in early winter can even produce thundersnow, snow showers accompanied by lightning and thunder.


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Wikipedia

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