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A hybrid Frontal-Lake Effect Snowsquall hitting Toronto, Canada during rush hour. Toronto lake effect frontal squall.JPG
A hybrid Frontal-Lake Effect Snowsquall hitting Toronto, Canada during rush hour.

A snowsquall, or snow squall, is a sudden moderately heavy snow fall with blowing snow and strong, gusty surface winds. [1] 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.

Lake-effect snow

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. [2] Whiteout conditions will affect narrow corridors from shores to inland areas aligned along the prevailing wind direction. [3] [4] 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. [5] Extremely cold air over still warm water in early winter can even produce thundersnow, snow showers accompanied by lightning and thunder.

Radar trace of lake-effect snowsqualls off the Great Lakes from US radars.
Snowsquall20101207 ontario.jpg
Radar image of a strong snowsquall off Lake Huron in December 2010. Over 150 cm of snow from this squall, fell north of London, Ontario. [6]
Lake effect snowsquall york region ontario jan08 03.jpg
A linear single banded snow squall over Southern Ontario

Frontal snowsquall

Frontal snowsquall moving toward Boston, Massachusetts, United States Snowsquall line-Bourrasque neige frontal NOAA.png
Frontal snowsquall moving toward Boston, Massachusetts, United States

A frontal snowsquall 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. [3] 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 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.


Rapidly deteriorating weather conditions during snowsqualls often lead to traffic accidents. Car into ditch bad winter weather hwy 404 south near stouffville rd Jan08.jpg
Rapidly deteriorating weather conditions during snowsqualls often lead to traffic accidents.
Winter conditions on Ontario Highway 401 in Toronto due to a snowsquall. Snowy Higddhway 4012.jpg
Winter conditions on Ontario Highway 401 in Toronto due to a snowsquall.

Both types of snowsqualls are very dangerous for motorists and airplanes or generally any traveler unfortunate enough to get stuck in one. The change in conditions is very sudden, and slippery conditions and abrupt loss of visibility due to whiteouts often cause multiple-vehicle collisions. 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. [7]

See also

Warnings about lake-effect snow:

United States

Related Research Articles

Lake-effect snow weather phenomenon

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 up by the lake water, picks up water vapor from the lake and rises up through the colder air above; the vapor then freezes and is deposited on the leeward (downwind) shores.

Surface weather analysis

Surface weather analysis is a special type of weather map that provides a view of weather elements over a geographical area at a specified time based on information from ground-based weather stations.

Squall sudden, sharp increase in the sustained winds over a short time interval

A squall is a sudden, sharp increase in wind speed lasting minutes, contrary to a wind gust lasting seconds. They are usually associated with active weather, such as rain showers, thunderstorms, or heavy snow. Squalls refer to the increase to the sustained winds over that time interval, as there may be higher gusts during a squall event. They usually occur in a region of strong sinking air or cooling in the mid-atmosphere. These force strong localized upward motions at the leading edge of the region of cooling, which then enhances local downward motions just in its wake.

Precipitation product of the condensation of atmospheric water vapour that falls under gravity

In meteorology, precipitation is any product of the condensation of atmospheric water vapour that falls under gravity. The main forms of precipitation include drizzle, rain, sleet, snow, graupel and hail. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor, so that the water condenses and "precipitates". Thus, fog and mist are not precipitation but suspensions, because the water vapor does not condense sufficiently to precipitate. Two processes, possibly acting together, can lead to air becoming saturated: cooling the air or adding water vapor to the air. Precipitation forms as smaller droplets coalesce via collision with other rain drops or ice crystals within a cloud. Short, intense periods of rain in scattered locations are called "showers."

Thundersnow Thunderstorm during which there is snowfall

Thundersnow, also known as a winter thunderstorm or a thundersnowstorm, is an unusual kind of thunderstorm with snow falling as the primary precipitation instead of rain. It typically falls in regions of strong upward motion within the cold sector of an extratropical cyclone. Thermodynamically, it is not different from any other type of thunderstorm, but the top of the cumulonimbus cloud is usually quite low. In addition to snow, graupel or hail may fall as well.

Alberta clipper storm system common to North America

An Alberta clipper, also known as a Canadian clipper, is a fast moving low pressure area weather system which generally affects the central provinces of Canada and parts of the Upper Midwest, Great Lakes, and New England, precipitating a sudden temperature drop and sharp winds. Alberta clippers take their name from Alberta, the province from which they appear to descend, and from clipper ships of the 19th century, one of the fastest ships of that time.

Panhandle hook

A panhandle hook is a relatively infrequent winter storm system whose cyclogenesis occurs in the South to southwestern United States from the late fall through winter and into the early spring months. They trek to the northeast on a path towards the Great Lakes region, as the southwesterly jet streams are most prevalent, usually affecting the Midwestern United States and Eastern Canada. Panhandle hooks account for some of the most memorable and deadly blizzards and snowstorms in North America. The name is derived from the region of surface cyclogenesis in the Texas panhandle and Oklahoma panhandle regions. In some winters, there are no panhandle hook storms; in others, there are several.

This is a list of meteorology topics. The terms relate to meteorology, the interdisciplinary scientific study of the atmosphere that focuses on weather processes and forecasting.

Weather front boundary separating two masses of air of different densities

A weather front is a boundary separating two masses of air of different densities, and is the principal cause of meteorological phenomena outside the tropics. In surface weather analyses, fronts are depicted using various colored triangles and half-circles, depending on the type of front. The air masses separated by a front usually differ in temperature and humidity.

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 States Department of Commerce (DoC), defines precise meanings for nearly all of its weather terms.


A rainband is a cloud and precipitation structure associated with an area of rainfall which is significantly elongated. Rainbands can be stratiform or convective, and are generated by differences in temperature. When noted on weather radar imagery, this precipitation elongation is referred to as banded structure. Rainbands within tropical cyclones are curved in orientation. Tropical cyclone rainbands contain showers and thunderstorms that, together with the eyewall and the eye, constitute a hurricane or tropical storm. The extent of rainbands around a tropical cyclone can help determine the cyclone's intensity.

Mesoscale convective system complex of thunderstorms organized on a larger scale

A mesoscale convective system (MCS) is a complex of thunderstorms that becomes organized on a scale larger than the individual thunderstorms but smaller than extratropical cyclones, and normally persists for several hours or more. A mesoscale convective system's overall cloud and precipitation pattern may be round or linear in shape, and include weather systems such as tropical cyclones, squall lines, lake-effect snow events, polar lows, and Mesoscale Convective Complexes (MCCs), and generally forms near weather fronts. The type that forms during the warm season over land has been noted across North America, Europe, and Asia, with a maximum in activity noted during the late afternoon and evening hours.

Mesoscale meteorology

Mesoscale meteorology is the study of weather systems smaller than synoptic scale systems but larger than microscale and storm-scale cumulus systems. Horizontal dimensions generally range from around 5 kilometers to several hundred kilometers. Examples of mesoscale weather systems are sea breezes, squall lines, and mesoscale convective complexes.

A Lake Effect Snow Warning is a bulletin issued by the National Weather Service in the United States to warn of heavy snowfall amounts that are imminent from convective snow generated by very cold airmass passing over unfrozen lakes. The criteria for amounts may vary significantly over different county warning areas. On October 2, 2017, some National Weather Service Forecast Offices discontinued issuing the Lake Effect Snow Warning, and consolidated it with the Winter Storm Warning. On October 15, 2018, the National Weather Service discontinued issuing Lake Effect Snow Warnings nationwide all together, and all offices consolidated it with the Winter Storm Warning. Lake Effect Snow Warnings were reinstated for the 2019–20 winter season.

Snow squall warning 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 events reducing visibility in blowing snow: Lake effectsnow squalls and Frontal snow squalls.

Extratropical cyclone type of cyclone

Extratropical cyclones, sometimes called mid-latitude cyclones or wave cyclones, are low-pressure areas which, along with the anticyclones of high-pressure areas, drive the weather over much of the Earth. Extratropical cyclones are capable of producing anything from cloudiness and mild showers to heavy gales, thunderstorms, blizzards, and tornadoes. These types of cyclones are defined as large scale (synoptic) low pressure weather systems that occur in the middle latitudes of the Earth. In contrast with tropical cyclones, extratropical cyclones produce rapid changes in temperature and dew point along broad lines, called weather fronts, about the center of the cyclone.

Cold front Leading edge of a cooler mass of air

A cold front is the leading edge of a cooler mass of air, replacing at ground level a warmer mass of air, which lies within a fairly sharp surface trough of low pressure. It forms in the wake of an extratropical cyclone, at the leading edge of its cold air advection pattern, which is also known as the cyclone's dry conveyor belt circulation. Temperature differences across the boundary can exceed 30 °C (54 °F) from one side to the other. When enough moisture is present, rain can occur along the boundary. If there is significant instability along the boundary, a narrow line of thunderstorms can form along the frontal zone. If instability is less, a broad shield of rain can move in behind the front, which increases the temperature difference across the boundary. Cold fronts are stronger in the fall and spring transition seasons and weakest during the summer.

Classifications of snow Methods for describing snowfall events and the resulting snow crystals

Classifications of snow describe and categorize the attributes of snow-generating weather events, including the individual crystals both in the air and on the ground, and the deposited snow pack as it changes over time. Snow can be classified by describing the weather event that is producing it, the shape of its ice crystals or flakes, how it collects on the ground, and thereafter how it changes form and composition. Depending on the status of the snow in the air or on the ground, a different classification applies.

2013–14 North American winter Winter in North America in 2013-2014

The 2013–14 North American winter refers to winter in North America as it occurred across the continent from late 2013 through early 2014. The winter of 2013–14 was one of the most significant for the United States, due in part to the breakdown of the polar vortex in November 2013, which allowed very cold air to travel down into the United States, leading to an extended period of very cold temperatures. The pattern continued mostly uninterrupted throughout the winter and numerous significant winter storms affected the Eastern United States, with the most notable one being a powerful winter storm that dumped ice and snow in the Southeast and Northeast in mid-February. Most of the cold weather abated by the end of March, though a few winter storms did affect the western portions of the U.S. towards the end of the winter.

Glossary of meteorology Wikimedia list article

This glossary of meteorology is a list of terms and concepts relevant to meteorology and atmospheric science, their sub-disciplines, and related fields.


  1. National Weather Service Detroit/Pontiac
  2. B. Geerts (1998). "Lake-Effect Snow". University of Wyoming . Retrieved 2008-12-24.
  3. 1 2 Meteorological Service of Canada (September 8, 2010). "Snow". Winter Hazards. Environment Canada . Retrieved 2010-10-04.
  4. Cameron Scott. "What is Lake-Effect Snow". Science 360!. RR Donnelly. Retrieved October 23, 2013.
  5. Jeff Haby. "Lake-effect forecasting". Haby's Weather Forecasting Hints. Retrieved 2009-08-12.
  6. "Snowstorm shuts down London Ontario". CBC News. CBC. December 8, 2010. Retrieved December 13, 2017.
  7. "Michigan I-94 Pileup | Firefighter Nation". Firefighter Nation. Retrieved 2015-10-09.