A snow squall, or snowsquall, is a sudden moderately heavy

snow Snow consists of individual ice crystals that grow while suspended in the atmosphere—usually within clouds—and then fall, accumulating on the ground where they undergo further changes. It consists of frozen crystalline water througho ...

fall with blowing snow and strong, gusty surface

wind Wind is the natural movement of atmosphere of Earth, air or other gases relative to a planetary surface, planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heatin ...

s. It is often referred to as a whiteout and is similar to a

blizzard A blizzard is a severe Winter storm, snowstorm characterized by strong sustained winds and low visibility, lasting for a prolonged period of time—typically at least three or four hours. A ground blizzard is a weather condition where snow th ...

but is localized in

time Time is the continuous progression of existence that occurs in an apparently irreversible process, irreversible succession from the past, through the present, and into the future. It is a component quantity of various measurements used to sequ ...

or in

location In geography, location or place is used to denote a region (point, line, or area) on Earth's surface. The term ''location'' generally implies a higher degree of certainty than ''place'', the latter often indicating an entity with an ambiguous bou ...

and snow accumulations may or may not be significant.

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,

convective Convection is single or multiphase fluid flow that occurs spontaneously through the combined effects of material property heterogeneity and body forces on a fluid, most commonly density and gravity (see buoyancy). When the cause of the convec ...

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 The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes spanning the Canada–United States border. The five lakes are Lake Superior, Superior, Lake Michigan, Michigan, Lake Huron, H ...

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

area of

North America North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...

, however any body of water can produce them. Regions in lee of

ocean The ocean is the body of salt water that covers approximately 70.8% of Earth. The ocean is conventionally divided into large bodies of water, which are also referred to as ''oceans'' (the Pacific, Atlantic, Indian Ocean, Indian, Southern Ocean ...

s, such as the Canadian

Maritimes The Maritimes, also called the Maritime provinces, is a region of Eastern Canada consisting of three provinces: New Brunswick, Nova Scotia, and Prince Edward Island. The Maritimes had a population of 1,899,324 in 2021, which makes up 5.1% of ...

could experience such snow squalls. The areas affected by lake-effect snow are called snowbelts and deposition rate of many

inches The inch (symbol: in or ) is a unit of length in the British Imperial and the United States customary systems of measurement. It is equal to yard or of a foot. Derived from the Roman uncia ("twelfth"), the word ''inch'' is also sometim ...

(

centimetre upright=1.35, Different lengths as in respect to the electromagnetic spectrum, measured by the metre and its derived scales. The microwave is in-between 1 meter to 1 millimeter. A centimetre (International spelling) or centimeter (American ...

s) of snow per hour are common in these situations. In order for lake-effect snow to form, the

temperature Temperature is a physical quantity that quantitatively expresses the attribute of hotness or coldness. Temperature is measurement, measured with a thermometer. It reflects the average kinetic energy of the vibrating and colliding atoms making ...

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 Wind shear (; also written windshear), sometimes referred to as wind gradient, is a difference in wind speed and/or direction over a relatively short distance in the atmosphere. Atmospheric wind shear is normally described as either vertical ...

with height should be less than 30° from the surface to . Extremely cold air over still warm water in early winter can even produce

thundersnow Thundersnow, also known as a winter thunderstorm or a thundersnow storm, is a thunderstorm in which snow falls as the primary precipitation instead of rain. It is considered a rare phenomenon. It typically falls in regions of strong upward moti ...

, snow showers accompanied by

lightning Lightning is a natural phenomenon consisting of electrostatic discharges occurring through the atmosphere between two electrically charged regions. One or both regions are within the atmosphere, with the second region sometimes occurring on ...

and

thunder Thunder is the sound caused by lightning. Depending upon the distance from and nature of the lightning, it can range from a long, low rumble to a sudden, loud crack. The sudden increase in temperature and hence pressure caused by the lightning pr ...

Frontal snow squall

Snowsquall line-Bourrasque neige frontal NOAA

A frontal snow squall is an intense frontal

line (similar to a

squall line A squall line, or quasi-linear convective system (QLCS), is a line of thunderstorms, often forming along or ahead of a cold front. In the early 20th century, the term was used as a synonym for cold front (which often are accompanied by abrupt a ...

), when

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 Trough may refer to: In science * Trough (geology), a long depression less steep than a trench * Trough (meteorology), an elongated region of low atmospheric pressure * Trough (physics), the lowest point on a wave * Trough level (medicine), the l ...

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

Dangers

Car into ditch bad winter weather hwy 404 south near stouffville rd Jan08

Both types of snow squalls are very dangerous for motorists,

airplanes An airplane (American English), or aeroplane (Commonwealth English), informally plane, is a fixed-wing aircraft that is propelled forward by thrust from a jet engine, propeller, or rocket engine. Airplanes come in a variety of sizes, shapes, ...

, and other

travel Travel is the movement of people between distant geographical Location (geography), locations. Travel can be done by Pedestrian, foot, bicycle, automobile, train, boat, bus, airplane, ship or other means, with or without Baggage, luggage, a ...

ers; even can be more dangerous than

s. The change in conditions is very sudden, with slippery conditions and abrupt loss of visibility due to whiteouts, which often cause

multiple-vehicle collision A multiple-vehicle collision (colloquially known as a pileup or multi-car collision), is a road traffic collision involving many vehicles. Generally occurring on high-capacity and high-speed routes such as freeways, they are one of the deadliest ...

s. In the case of

lake-effect snow Lake-effect snow is produced during cooler atmospheric conditions when a cold air mass moves across long expanses of warmer lake water. The lower layer of air, heated by the lake water, picks up water vapor from the lake and rises through colde ...

, heavy amounts of snow can accumulate in short periods of time, possibly causing road closures and paralyzing cities. For instance, on January 9, 2015, a localized, heavy snow squall caused a 193-vehicle pile-up on I-94 highway near Galesburg, Michigan. On very rare occasions, particularly powerful snow squalls can even become supercells and form

tornado A tornado is a violently rotating column of air that is in contact with the surface of Earth and a cumulonimbus cloud or, in rare cases, the base of a cumulus cloud. It is often referred to as a twister, whirlwind or cyclone, although the ...

es, even if no lightning or

is present.

References

External links

{{Commons, Snow
Winter Weather Awareness
by the US

National Weather Service The National Weather Service (NWS) is an Government agency, agency of the Federal government of the United States, United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weathe ...