![Toronto lake effect frontal squall](https://upload.wikimedia.org/wikipedia/commons/0/0f/Toronto_lake_effect_frontal_squall.JPG)
A snowsquall, or snow squall, is a sudden moderately heavy
snow
Snow comprises 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 throughout ...
fall with
blowing snow
Blowing snow is snow lifted from the surface by the wind, at eye level () or more, that will reduce visibility. Blowing snow can come from falling snow or snow that already accumulated on the ground but is picked up and blown about by strong winds. ...
and strong, gusty surface
wind
Wind is the natural movement of air or other gases relative to a planet's surface. Winds occur on a range of scales, from thunderstorm flows lasting tens of minutes, to local breezes generated by heating of land surfaces and lasting a few ho ...
s. It is often referred to as a
whiteout and is similar to a
blizzard
A blizzard is a severe 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 is not falling ...
but is localized in
time
Time is the continued sequence of existence and events that occurs in an apparently irreversible succession from the past, through the present, into the future. It is a component quantity of various measurements used to sequence events, ...
or in
location
In geography, location or place are used to denote a region (point, line, or area) on Earth's surface or elsewhere. The term ''location'' generally implies a higher degree of certainty than ''place'', the latter often indicating an entity with an ...
and snow accumulations may or may not be significant.
Types
There are two primary types of snowsqualls: lake effect and frontal.
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 due to 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 in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five lak ...
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
In meteorology, prevailing wind in a region of the Earth's surface is a surface wind that blows predominantly from a particular direction. The dominant winds are the trends in direction of wind with the highest speed over a particular point o ...
direction.
This will be enhanced when the moving air mass is
uplifted
''Uplifted'' is the second studio album by Nigerian singer Flavour N'abania. It was released on July 20, 2010, by Obaino Music and 2nite Entertainment. The album features guest appearances from Jay Dey, Oloye, Stormrex, Waga Gee, Asemstone, M-Jay, ...
by higher elevations. The name originates from the
Great Lakes
The Great Lakes, also called the Great Lakes of North America, are a series of large interconnected freshwater lakes in the mid-east region of North America that connect to the Atlantic Ocean via the Saint Lawrence River. There are five lak ...
area of
North America, however any body of water can produce them. Regions in
lee of
ocean
The ocean (also the sea or the world ocean) is the body of salt water that covers approximately 70.8% of the surface of Earth and contains 97% of Earth's water. An ocean can also refer to any of the large bodies of water into which the wo ...
s, such as the Canadian
Maritimes could experience such snowsqualls.
The areas affected by lake-effect snow are called
snowbelt
The Snowbelt is the region near the Great Lakes in North America where heavy snowfall in the form of lake-effect snow is particularly common. Snowbelts are typically found downwind of the lakes, principally off the eastern and southern shores.
Ca ...
s and deposition rate of many
inches
Measuring tape with 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") ...
(
centimetre
330px, Different lengths as in respect to the Electromagnetic spectrum, measured by the Metre and its deriveds scales. The Microwave are in-between 1 meter to 1 millimeter.
A centimetre (international spelling) or centimeter (American spellin ...
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 expresses quantitatively the perceptions of hotness and coldness. Temperature is measurement, measured with a thermometer.
Thermometers are calibrated in various Conversion of units of temperature, temp ...
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 (or 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 or horizont ...
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 thundersnowstorm, is a kind of thunderstorm with snow falling as the primary precipitation instead of rain. It is considered a rare and unusual phenomenon. It typically falls in regions of s ...
, snow showers accompanied by
lightning
Lightning is a naturally occurring electrostatic discharge during which two electrically charged regions, both in the atmosphere or with one on the ground, temporarily neutralize themselves, causing the instantaneous release of an avera ...
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 snowsquall
![Snowsquall line-Bourrasque neige frontal NOAA](https://upload.wikimedia.org/wikipedia/commons/c/cb/Snowsquall_line-Bourrasque_neige_frontal_NOAA.png)
A frontal snowsquall is an intense frontal
convective
Convection is single or multiphase fluid flow that occurs spontaneously due to 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 ...
line (similar to a
squall line
A squall line, or more accurately a 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 accom ...
), when
temperature
Temperature is a physical quantity that expresses quantitatively the perceptions of hotness and coldness. Temperature is measurement, measured with a thermometer.
Thermometers are calibrated in various Conversion of units of temperature, temp ...
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 snowsquall 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 25 miles (40 kilometers) 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 5,000 to 10,000 feet (1,500 to 3,000 m), 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 30 knots (55.58 km/h). However, the cold dome behind the trough is at 850 mbar instead of a higher level and must be at least -13 °F (-25 °C). 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
In meteorology, convective available potential energy (commonly abbreviated as CAPE), is the integrated amount of work that the upward (positive) buoyancy force would perform on a given mass of air (called an air parcel) if it rose vertically thro ...
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
Thundersnow, also known as a winter thunderstorm or a thundersnowstorm, is a kind of thunderstorm with snow falling as the primary precipitation instead of rain. It is considered a rare and unusual phenomenon. It typically falls in regions of s ...
.
Dangers
Both types of snowsqualls are very dangerous for motorists
Driving is the controlled operation and movement of a vehicle, including cars, motorcycles, trucks, buses, and bicycles. Permission to drive on public highways is granted based on a set of conditions being met and drivers are required to fol ...
, airplanes
An airplane or aeroplane (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 wing configurations. The broad spectr ...
, and other travel
Travel is the movement of people between distant geographical locations. Travel can be done by foot, bicycle, automobile, train, boat, bus, airplane, ship or other means, with or without luggage, and can be one way or round trip. Travel c ...
ers; even can be more dangerous than blizzard
A blizzard is a severe 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 is not falling ...
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 pile-up, multi-car collision, multi-vehicle collision, or simply a multi) is a road traffic collision involving many vehicles. Generally occurring on high-capacity and high-speed routes such ...
s. In the case of lake-effect snow, 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.
See also
*Convection
Convection is single or multiphase fluid flow that occurs spontaneously due to 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 conve ...
*Snow shower
A shower is a mode of precipitation characterized by an abrupt start and end and by rapid variations in intensity. Often strong and short-lived, it comes from convective clouds, like cumulus congestus. A shower will produce rain if the temperatu ...
Warnings about lake-effect snow:
;United States
* Lake Effect Snow Advisory
* Lake Effect Snow Warning
*Severe weather terminology (United States)
This article describes severe weather terminology used by the National Weather Service (NWS) in the United States. The NWS, a government agency operating as an arm of the National Oceanic and Atmospheric Administration (NOAA) branch of the United ...
* Snowsquall warning
;Canada
*Snow Squall Warning
A snow squall warning (Specific Area Message Encoding, SAME code: SQW) is a bulletin issued by Environment Canada's Meteorological Service of Canada and the National Weather Service in the United States to warn population of two types of snow eve ...
*Severe weather terminology (Canada)
This article describes severe weather terminology used by the Meteorological Service of Canada, a branch within Environment and Climate Change Canada. The article primarily describes various weather warnings, and their criteria. Related weather s ...
References
External links
{{Commons, Snow
Winter Weather Awareness
by the US National Weather Service
The National Weather Service (NWS) is an agency of the United States federal government that is tasked with providing weather forecasts, warnings of hazardous weather, and other weather-related products to organizations and the public for the ...
Environment Canada - Weather and Meteorology - Hazardous weather-winter hazards
Video of a snowsquall timelapse while driving on Highway 407 ETR in Greater Toronto
Weather hazards
Snow or ice weather phenomena
de:Lake effect snow