A snow squall, or snowsquall, is a sudden moderately heavy with blowing snow and strong, gusty surface .
Types
There are two primary types of snow squalls: lake effect and frontal. Both types can strongly reduce visibilities and sometimes produce heavy snowfall.
Lake-effect snow
When arctic air moves over large expanses of warmer open waters in winter,
convection 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 winds direction.
This will be enhanced when the moving air mass is
Orographic lift 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
, such as the Canadian
Maritimes could experience such snow squalls.
The areas affected by lake-effect snow are called and deposition rate of many inches () of snow per hour are common in these situations. In order for lake-effect snow to form, the temperature difference between the water and should be at least , surface temperature be around the freezing mark, the lake unfrozen, the path over the lake at least and the directional wind shear with height should be less than 30° from the surface to .
Frontal snow squall
A frontal snow squall is an intense frontal
convective line (similar to a
squall line), when
temperature is near freezing at the surface. The strong convection that develops has enough moisture to produce whiteout conditions at places which line passes over as the wind causes intense blowing snow.
[ This type of snow squall generally lasts less than 30 minutes at any point along its path but the motion of the line can cover large distances. Frontal squalls may form a short distance ahead of the surface cold front or behind the cold front in situations where there are other contributing factors such as dynamic lifting from a deepening low pressure system or a series of trough lines which act similar to a traditional cold frontal passage. In situations where squalls develop post-frontally it is not unusual to have two or three linear squall bands pass in rapid succession only separated by with each passing the same point in roughly 30 minutes apart.
]
This is similar to a line of thunderstorms in the summer but the tops of the clouds are only , often difficult to see on radar. Forecasting these types of events 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 . However, the cold dome behind the trough is at 850 millibars instead of a higher level and must be at least . The presence of surface moisture from bodies of water or preexisting liquid precipitation is also a significant contributing factor helping to raise the dew point temperature and saturate the boundary layer. This saturate can significantly increase the amount of convective available potential energy leading to deeper vertical growth and higher precipitable water levels increasing the volume of snow which can be produced by the squall. In cases where there is a large amount of vertical growth and mixing the squall may develop embedded cumulonimbus clouds resulting in lightning and thunder which is dubbed thundersnow.
Dangers
Both types of snow squalls are very dangerous for Driving, airplanes, and other ; even can be more dangerous than .
See also
Warnings about lake-effect snow:
- United States
-
Lake Effect Snow Advisory
-
Lake Effect Snow Warning
-
Severe weather terminology (United States)
-
Snow squall warning
- Canada
-
Snow Squall Warning
-
Severe weather terminology (Canada)
External links
