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A snowsquall, or snow squall, is a sudden moderately heavy snowfall 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 millibars (850 hPa) 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 kilometres (62 mi) and the directional wind shear with height should be less than 30° from the surface to 850 millibars (850 hPa). Extremely cold air over still warm water in early winter can even produce thundersnow, snow showers accompanied by lightning and thunder.
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.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.
Both types of snowsqualls are very dangerous for motorists, airplanes, and other travelers; even can be more dangerous than blizzards.The change in conditions is very sudden, with slippery conditions and abrupt loss of visibility due to whiteouts, which 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.
Warnings about 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 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.
The 1993 Storm of the Century was a cyclonic storm that formed over the Gulf of Mexico on March 12, 1993. The cold weather, heavy snowfall, high winds and storm surges that the storm brought affected a very large area; at its height, it stretched from Canada to Honduras. The cyclone moved through the Gulf of Mexico and then through the eastern United States before moving on to eastern Canada. It eventually dissipated in the North Atlantic Ocean on March 15.
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 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.
An Alberta clipper, also known as an Alberta low, Alberta cyclone, Alberta lee cyclone, Canadian clipper, or simply clipper, is a fast-moving low-pressure system that originates in or near the Canadian province of Alberta just east of the Rocky Mountains and tracks east-southeastward across southern Canada and the northern United States to the North Atlantic Ocean.
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.
A weather front is a boundary separating air masses for which several characteristics differ, such as air density, wind, temperature, and humidity. Disturbed and unstable weather due to these differences often arises along the boundary. For instance, cold fronts can bring bands of thunderstorms and cumulonimbus precipitation or be preceded by squall lines, while warm fronts are usually preceded by stratiform precipitation and fog. In summer, subtler humidity gradients known as dry lines can trigger severe weather. Some fronts produce no precipitation and little cloudiness, although there is invariably always a wind shift.
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. Rainbands of tropical cyclones 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.
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 and South America, Europe, and Asia, with a maximum in activity noted during the late afternoon and evening hours.
A 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 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 severe 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.
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. It is one of the classic requirements for a blizzard. Its METAR code is BLSN. If the snow remains below 1.8 m (6 ft), it will be called drifting snow. The snow which is being blown about may deposit as snowdrifts.
A cold front is the leading edge of a cooler mass of air at ground level that replaces a warmer mass of air and lies within a pronounced surface trough of low pressure. It often forms behind an extratropical cyclone, at the leading edge of its cold air advection pattern—known as the cyclone's dry "conveyor belt" flow. 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 weak, a broad shield of rain can move in behind the front, and evaporative cooling of the rain can increase the temperature difference across the front. Cold fronts are stronger in the fall and spring transition seasons and are weakest during the summer.
The 2013–14 North American winter 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.
At the start of spring 2016, a major winter storm moved through the High Plains and Midwest, bringing blizzard conditions with snowfall of up to 12–18 inches (30–46 cm) and strong winds as well. Snowstorms like this are typical in these areas at this time of year. The system also brought with it a severe weather threat as well. As it moved to the east, a crippling ice storm scenario was developing as well.
The 2012–13 North American winter started out somewhat early, as the remnants of Hurricane Sandy brought heavy snow to the mountains of West Virginia in late October. Later, a strong nor'easter affected the weary Northeast, hampering storm recovery efforts and dropping several inches of snow. The rest of the winter featured several other notable events, such as a Christmas winter storm that affected most of the eastern part of the country, and the most notable event occurring in early February, when a powerful blizzard struck the Northeast and bringing record snow to some areas. During the winter, a weak El Nino was expected to influence weather conditions across the continent.
This glossary of meteorology is a list of terms and concepts relevant to meteorology and atmospheric science, their sub-disciplines, and related fields.
The April 2021 nor'easter, also referred to as the 2021 Spring nor'easter, was a significant late-season nor'easter that impacted much of New England with heavy snowfall, gusty winds, thundersnow, and near-whiteout conditions from April 15–17, 2021. The system originated from a weak frontal system late on April 14 over North Carolina, which moved into the ocean the next day and began to strengthen. The low-pressure steadily deepened as it moved up the East Coast, and developed an eye-like feature just prior to peak intensity. It prompted a fairly large area of Winter Storm Warnings across interior sections of New England, with Winter Weather Advisories being issued closer to the coast. Over 20,000 customers lost power at the height of the storm on April 16 due to heavy wet snow, and near-whiteout conditions were reported in many areas. Several injuries, some serious, occurred as well, mostly due to traffic incidents on poorly-treated roadways during the storm. Damage estimates from the system are currently not calculated.
Elpis, or Elpida in Greece, was a windstorm and blizzard that affected most of the Eastern Mediterranean. The storm caused blizzard conditions in northern Turkey and mountainous areas of Greece, as well as accumulating snowfall in milder locations further south, such as Athens, Antalya and Israel.