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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 colder air. The vapor then freezes and is deposited on the leeward (downwind) shores. [1]
The same effect also occurs over bodies of saline water, when it is termed ocean-effect or bay-effect snow. The effect is enhanced when the moving air mass is uplifted by the orographic influence of higher elevations on the downwind shores. This uplifting can produce narrow but very intense bands of precipitation, which deposit at a rate of many inches of snow each hour, often resulting in a large amount of total snowfall.
The areas affected by lake-effect and parallel "ocean-effect" phenomena are called snowbelts. These include areas east of the Great Lakes in North America, the west coasts of northern Japan, Lake Baikal in Russia, and areas near the Great Salt Lake, Black Sea, Caspian Sea, Baltic Sea, Adriatic Sea, the North Sea and more.
Lake-effect blizzards are the blizzard-like conditions resulting from lake-effect snow. Under certain conditions, strong winds can accompany lake-effect snows creating blizzard-like conditions; however, the duration of the event is often slightly less than that required for a blizzard warning in both the U.S. and Canada. [2]
If the air temperature is low enough to keep the precipitation frozen, it falls as lake-effect snow. If not, then it falls as lake-effect rain. For lake-effect rain or snow to form, the air moving across the lake must be significantly cooler than the surface air (which is likely to be near the temperature of the water surface). Specifically, the air temperature at an altitude where the air pressure is 850 millibars (85 kPa ) (roughly 1.5 kilometers or 5,000 feet vertically) should be 13 °C (23 °F) lower than the temperature of the air at the surface. Lake-effect occurring when the air at 850 millibars (85 kPa ) is much colder than the water surface can produce thundersnow, snow showers accompanied by lightning and thunder (caused by larger amounts of energy available from the increased instability).
Some key elements are required to form lake-effect precipitation and which determine its characteristics: instability, fetch, wind shear, upstream moisture, upwind lakes, synoptic (large)-scale forcing, orography/topography, and snow or ice cover.
A temperature difference of approximately 13 °C (23 °F) between the lake temperature and the height in the atmosphere (about 1,500 m or 5,000 ft at which barometric pressure measures 850 mbar or 85 kPa) provides for absolute instability and allows vigorous heat and moisture transportation vertically. Atmospheric lapse rate and convective depth are directly affected by both the mesoscale lake environment and the synoptic environment; a deeper convective depth with increasingly steep lapse rates and a suitable moisture level allow for thicker, taller lake-effect precipitation clouds and naturally a much greater precipitation rate. [3]
The distance that an air mass travels over a body of water is called fetch. Because most lakes are irregular in shape, different angular degrees of travel yield different distances; typically, a fetch of at least 100 km (60 mi) is required to produce lake-effect precipitation. Generally, the larger the fetch, the more precipitation produced. Larger fetches provide the boundary layer with more time to become saturated with water vapor and for heat energy to move from the water to the air. As the air mass reaches the other side of the lake, the engine of rising and cooling water vapor pans itself out in the form of condensation and falls as snow, usually within 40 km (25 mi) of the lake, but sometimes up to about 150 km (100 mi). [4]
Directional shear is one of the most important factors governing the development of squalls; environments with weak directional shear typically produce more intense squalls than those with higher shear levels. If directional shear between the surface and the height in the atmosphere at which the barometric pressure measures 700 mb (70 kPa) is greater than 60°, nothing more than flurries can be expected. If the directional shear between the body of water and the vertical height at which the pressure measures 700 mb (70 kPa) is between 30° and 60°, weak lake-effect bands are possible. In environments where the shear is less than 30°, strong, well organized bands can be expected. [5]
Speed shear is less critical but should be relatively uniform. The wind-speed difference between the surface and vertical height at which the pressure reads 700 mb (70 kPa) should be no greater than 40 knots (74 km/h) so as to prevent the upper portions of the band from shearing off. However, assuming the surface to 700 mb (70 kPa) winds are uniform, a faster overall velocity works to transport moisture more quickly from the water, and the band then travels much farther inland. [5]
A lower upstream relative humidity lake effect makes condensation, clouds, and precipitation more difficult to form. The opposite is true if the upstream moisture has a high relative humidity, allowing lake-effect condensation, cloud, and precipitation to form more readily and in a greater quantity. [6]
Any large body of water upwind impacts lake-effect precipitation to the lee of a downwind lake by adding moisture or pre-existing lake-effect bands, which can reintensify over the downwind lake. Upwind lakes do not always lead to an increase of precipitation downwind. [7]
Vorticity advection aloft and large upscale ascent help increase mixing and the convective depth, while cold air advection lowers the temperature and increases instability. [8]
Typically, lake-effect precipitation increases with elevation to the lee of the lake as topographic forcing squeezes out precipitation and dries out the squall much faster. [9]
As a lake gradually freezes over, its ability to produce lake-effect precipitation decreases for two reasons. Firstly, the open ice-free liquid surface area of the lake shrinks. This reduces fetch distances. Secondly, the water temperature nears freezing, reducing overall latent heat energy available to produce squalls. To end the production of lake-effect precipitation, a complete freeze is often not necessary. [10]
Even when precipitation is not produced, cold air passing over warmer water may produce cloud cover. Fast-moving mid-latitude cyclones, known as Alberta clippers, often cross the Great Lakes. After the passage of a cold front, winds tend to switch to the northwest, and a frequent pattern is for a long-lasting low-pressure area to form over the Canadian Maritimes, which may pull cold northwestern air across the Great Lakes for a week or more, commonly identified with the negative phase of the North Atlantic Oscillation (NAO). Since the prevailing winter winds tend to be colder than the water for much of the winter, the southeastern shores of the lakes are almost constantly overcast, leading to the use of the term "the Great Gray Funk" as a synonym for winter.[ citation needed ] These areas allegedly contain populations that suffer from high rates of seasonal affective disorder, a type of psychological depression thought to be caused by lack of light. [11] [ citation needed ]
Cold winds in the winter typically prevail from the northwest in the Great Lakes region, producing the most dramatic lake-effect snowfalls on the southern and eastern shores of the Great Lakes. This lake effect results in much greater snowfall amounts on the southern and eastern shores compared to the northern and western shores of the Great Lakes.
The most affected areas include the Upper Peninsula of Michigan; Northern New York and Central New York; particularly the Tug Hill Region, Western New York; Northwestern Pennsylvania; Northeastern Ohio; southwestern Ontario and central Ontario; Northeastern Illinois (along the shoreline of Lake Michigan); northwestern and north central Indiana (mostly between Gary and Elkhart); northern Wisconsin (near Lake Superior); and West Michigan. [12]
Lake-effect snows on the Tug Hill plateau (east of Lake Ontario) can frequently set daily records for snowfall in the United States. Tug Hill receives, typically, over 20 feet (240 in; 610 cm) of snow each winter. [13] The snowiest portions of the Tug Hill, near the junction of the towns of Montague, Osceola, Redfield, and Worth, average over 300 inches (760 cm) of snow annually. [14]
From February 3–12, 2007, a lake-effect snow event left 141 inches (358 cm) of snow in 10 days at North Redfield on the Tug Hill Plateau. [15] [16] Other examples major prolonged lake effect snowstorms on the Tug Hill include December 27, 2001, - January 1, 2002, when 127 inches (320 cm) of snow fell in six days in Montague, January 10–14, 1997, when 110.5 inches (281 cm) of snow fell in five days in North Redfield, and January 15–22, 1940, when over eight feet of snow fell in eight days at Barnes Corners. [16]
Syracuse, New York, directly south of the Tug Hill Plateau, receives significant lake-effect snow from Lake Ontario, and averages 115.6 inches (294 cm) of snow per year, which is enough snowfall to be considered one of the "snowiest" large cities in America. [17] [18]
Lake Erie produces a similar effect for a zone stretching from the eastern suburbs of Cleveland through Erie to Buffalo. [19] Remnants of lake-effect snows from Lake Erie have been observed to reach as far south as Garrett County, Maryland, and as far east as Geneva, New York. [20] Because it is not as deep as the other lakes, Erie warms rapidly in the spring and summer, and is frequently the only Great Lake to freeze over in winter. [21] Once frozen, the resulting ice cover alleviates lake-effect snow downwind of the lake. Based on stable isotope evidence from lake sediment coupled with historical records of increasing lake-effect snow, global warming has been predicted to result in a further increase in lake-effect snow. [22]
A very large snowbelt in the United States exists on the Upper Peninsula of Michigan, near the cities of Houghton, Marquette, and Munising. These areas typically receive 250–300 inches (635–762 cm) of snow each season. [23] For comparison, on the western shore, Duluth, Minnesota receives 78 inches (198 cm) per season. [24]
Western Michigan, western Northern Lower Michigan, and Northern Indiana can get heavy lake-effect snows as winds pass over Lake Michigan and deposit snows over Muskegon, Traverse City, Grand Rapids, Kalamazoo, New Carlisle, South Bend, and Elkhart, but these snows abate significantly before Lansing or Fort Wayne, Indiana. When winds become northerly or aligned between 330 and 390°, a single band of lake-effect snow may form, which extends down the length of Lake Michigan. This long fetch often produces a very intense, yet localized, area of heavy snowfall, affecting cities such as La Porte and Gary. [25]
Lake-effect snow is virtually unheard of in Detroit, Toledo, Milwaukee, Toronto, and Chicago, because the region's dominant winds are from the northwest, making them upwind from their respective Great Lakes, although they, too, have on extremely rare occasion seen small amounts of lake-effect snow during easterly or northeasterly winds. More frequently, the north side of a low-pressure system picks up more moisture over the lake as it travels east, creating a phenomenon called lake-enhanced precipitation. [25] However, a place like Altoona, Pennsylvania or Oakland, Maryland is far more likely to receive lake effect snow than either aforementioned location despite greater distance from the lakes, because of being on the leeward side of the lake.
Because Southwestern Ontario is surrounded by water on three sides, many parts of Southwestern and Central Ontario get a large part of their winter snow from lake-effect snow. [26] This region is notorious for the whiteouts that can suddenly reduce highway visibility on North America's busiest highway (Ontario Highway 401) [27] from clear to zero. The region most commonly affected spans from Port Stanley in the west, the Bruce Peninsula in the north, Niagara-on-the-Lake to the east, and Fort Erie to the south. The heaviest accumulations usually happen in the Bruce Peninsula, which is between Lake Huron and Georgian Bay. So long as the Great Lakes are not frozen over, the only time the Bruce Peninsula does not get lake-effect snow is when the wind is directly from the south.
The southern and southeastern sides of the Great Salt Lake receive significant lake-effect snow. Since the Great Salt Lake never freezes, the lake effect can influence the weather along the Wasatch Front year-round. The lake effect largely contributes to the 55–80 inches (140–203 cm) annual snowfall amounts recorded south and east of the lake, and in average snowfall reaching 500 inches (13 m) in the Wasatch Range. The snow, which is often very light and dry because of the semiarid climate, is referred to as the "Greatest Snow on Earth" in the mountains. Lake-effect snow contributes to roughly six to eight snowfalls per year in Salt Lake City, with about 10% of the city's precipitation being contributed by the phenomenon. [28]
On one occasion in December 2016, lake-effect snow fell in central Mississippi from a lake band off Ross Barnett Reservoir. [29]
The West Coast occasionally experiences ocean-effect showers, usually in the form of rain at lower elevations south of about the mouth of the Columbia River. These occur whenever an Arctic air mass from western Canada is drawn westward out over the Pacific Ocean, typically by way of the Fraser Valley, returning shoreward around a center of low pressure. Cold air flowing southwest from the Fraser Valley can also pick up moisture over the Strait of Georgia and Strait of Juan de Fuca, then rise over the northeastern slopes of the Olympic Mountains, producing heavy, localized snow between Port Angeles and Sequim, as well as areas in Kitsap County and the Puget Sound region. [30]
While snow of any type is very rare in Florida, the phenomenon of gulf-effect snow has been observed along the northern coast of the Gulf of Mexico a few times in history. More recently, "ocean-effect" snow occurred on January 24, 2003, when wind off the Atlantic, combined with air temperatures in the 30 °F range, brought snow flurries briefly to the Atlantic Coast of northern Florida seen in the air as far south as Cape Canaveral. [31]
Because the southern Black Sea is relatively warm (around 13 °C or 55 °F at the beginning of winter, typically 10 to 6 °C or 50 to 43 °F by the end), sufficiently cold air aloft can create significant snowfalls in a relatively short period of time. [32] Furthermore, cold air, when it arrives to the region, tends to move slowly, creating days and sometimes weeks of occasional lake-effect snowfall. [32]
The most populous city in the region, Istanbul, is very prone to lake-effect snow and this weather phenomenon occurs almost every winter, despite winter averages or 5 °C (41 °F), comparable to Paris. [33] On multiple occasions, lake-effect snowfall events have lasted for more than a week, and official single-storm snow depth totals have exceeded 80 centimeters (2.6 ft; 31 in) downtown and 104 centimeters (3.41 ft; 41 in) around the city. [34] [33] [35] Earlier, unofficial measurements are often higher, due to the relative dearth of sufficiently old weather stations in the region; some sources claim up to 4 meters (13 ft; 160 in) of snowfall during the blizzard of March 1987. [36]
Meanwhile, snowfall in mountainous provinces in this region is amplified by orographic effect, often resulting in snowfall of several meters, especially at higher elevations.
In Northern Europe, cold, dry air masses from Russia can blow over the Baltic Sea and cause heavy snow squalls on areas of the southern and eastern coasts of Sweden, as well as on the Danish island of Bornholm, the east coast of Jutland and the northern coast of Poland. For the northern parts of the Baltic Sea, this happens mainly in the early winter, since it freezes later. Southeast Norway can also experience heavy sea snow events with east-north-easterly winds. Especially, coastal areas from Kragero to Kristiansand have had incredible snow depths in the past with intense persistent snowbands from Norwegian Sea (the coastal city of Arendal recorded 280 cm (110 in) in a single week in late February 2007). [37] Although Fennoscandia is lined with an abundance of lakes, this type of snowfall is rare in these, due to the shallow freshwater freezing early in the cold interiors. One notable exception happened in the middle of May 2008, as Leksand on the since-long unfrozen lake of Siljan got 30 cm (12 in) on the ground. [38]
The Sea of Japan creates snowfall in the mountainous western Japanese prefectures of Niigata and Nagano, parts of which are known collectively as snow country (Yukiguni). In addition to Japan, much of maritime Korea and the Shandong Peninsula experience these conditions. [39]
Strong winds and a very large, deep lake enhance snowfall around Lake Baikal in the fall; however, nearly the entire surface of the lake freezes from January until Spring, precluding lake-effect snow. [40]
Moving of polar or Siberian high-pressure centers along Caspian Sea regarding to relatively warmer water of this sea can make heavy snowfalls in the northern coast of Iran. Several blizzards have been reported in this region during the last decades. In February 2014, heavy snowfall reached 200 cm (79 in) on the coastline in Gilan and Mazandaran provinces of Iran. The heaviest snowfall was reported in Abkenar village near Anzali Lagoon. [41] [42] [43] [44]
In the United Kingdom, easterly winds bringing cold continental air across the North Sea can lead to a similar phenomenon. Locally, it is also known as "lake-effect snow" despite the snow coming in from the sea rather than a lake. [46] Similarly during a north-westerly wind, snow showers can form coming in from the Liverpool Bay, coming down the Cheshire gap, causing snowfall in the West Midlands—this formation resulted in the white Christmas of 2004 in the area, and most recently the heavy snowfall of 8 December 2017 and 30 January 2019. [47] [48]
The best-known example occurred in January 1987, when record-breaking cold air (associated with an upper low) moved across the North Sea towards the UK. The result was over 2 ft of snow for coastal areas, leading to communities being cut off for over a week. The latest of these events to affect Britain's east coast occurred on November 30, 2017; February 28, 2018; and March 17, 2018; in connection with the 2018 Great Britain and Ireland cold wave. [49] The second event of winter 2017/18 was particularly severe, with up to 27.5 inches (70 cm) falling in total over the 27th–28th. [50]
Similarly, northerly winds blowing across the relatively warm waters of the English Channel during cold spells can bring significant snowfall to the French region of Normandy, where snow drifts exceeding 10 ft (3 m) were measured in March 2013. [51]
Warnings about lake-effect 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 its life cycle, starting when, under suitable conditions, the ice crystals form in the atmosphere, increase to millimeter size, precipitate and accumulate on surfaces, then metamorphose in place, and ultimately melt, slide or sublimate away.
A winter storm is an event in which wind coincides with varieties of precipitation that only occur at freezing temperatures, such as snow, mixed snow and rain, or freezing rain. In temperate continental and subarctic climates, these storms are not necessarily restricted to the winter season, but may occur in the late autumn and early spring as well. A snowstorm with strong winds and other conditions meeting certain criteria is called a blizzard.
In meteorology, precipitation is any product of the condensation of atmospheric water vapor that falls from clouds due to gravitational pull. The main forms of precipitation include drizzle, rain, sleet, snow, ice pellets, graupel and hail. Precipitation occurs when a portion of the atmosphere becomes saturated with water vapor, so that the water condenses and "precipitates" or falls. Thus, fog and mist are not precipitation; their water vapor does not condense sufficiently to precipitate, so fog and mist do not fall. Two processes, possibly acting together, can lead to air becoming saturated with water vapor: 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.
The Snowbelt, Snow Belt, Frostbelt, or Frost Belt 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.
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 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. The heavy snowfall tends to muffle the sound of the thunder so that it sounds more like a low rumble than the loud, sharp bang that is heard during regular thunderstorms.
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.
The climate of Salt Lake City, Utah features cold and snowy winters, hot and dry summers, and modest to light seasonal rainfall. Lying in the Salt Lake Valley, the city is surrounded by mountains and the Great Salt Lake. Under the Köppen climate classification, Salt Lake City has either a Mediterranean climate (Csa) or dry-summer continental climate (Dsa) depending on which variant of the system is used, though it borders on a cold semi-arid climate (BSk) due to the city's relatively low precipitation.
A rainband is a cloud and precipitation structure associated with an area of rainfall which is significantly elongated. Rainbands in tropical cyclones can be either stratiform or convective and are curved in shape. They consist of showers and thunderstorms, and along with the eyewall and the eye, they make up a tropical cyclone. 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, or snowsquall, 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.
Milwaukee has a humid continental climate, with four distinct seasons and wide variations in temperature and precipitation in short periods of time. The city's climate is also strongly influenced by nearby Lake Michigan, which creates two varying climates within the Milwaukee area. The urban heat island effect also plays a role in the city's climate, insulating it from winter cold, but keeping it cooler in spring and summer.
Minnesota has a humid continental climate, with hot summers and cold winters. Minnesota's location in the Upper Midwest allows it to experience some of the widest variety of weather in the United States, with each of the four seasons having its own distinct characteristics. The area near Lake Superior in the Minnesota Arrowhead region experiences weather unique from the rest of the state. The moderating effect of Lake Superior keeps the surrounding area relatively cooler in the summer and warmer in the winter, giving that region a smaller yearly temperature variation. On the Köppen climate classification, much of the southern third of Minnesota—roughly from the Twin Cities region southward—falls in the hot summer zone (Dfa), and the northern two-thirds of Minnesota falls in the warm summer zone (Dfb).
The characteristics of United States rainfall climatology differ significantly across the United States and those under United States sovereignty. Summer and early fall bring brief, but frequent thundershowers and tropical cyclones which create a wet summer and drier winter in the eastern Gulf and lower East Coast. During the winter, and spring, Pacific storm systems bring Hawaii and the western United States most of their precipitation. Low pressure systems moving up the East Coast and through the Great Lakes, bring cold season precipitation to from the Midwest to New England, as well as Great Salt Lake. The snow to liquid ratio across the contiguous United States averages 13:1, meaning 13 inches (330 mm) of snow melts down to 1 inch (25 mm) of water.
The Great Salt Lake effect is a small but detectable influence on the local climate and weather around the Great Salt Lake in Utah, United States. In particular, snowstorms are a common occurrence over the region and have major socio-economic impacts due to their significant precipitation amounts. The Great Salt Lake almost never freezes and can warm rapidly, which allows lake enhanced precipitation to occur from September through May. Lake-enhanced snowstorms are often attributed to creating what is locally known as "The Greatest Snow on Earth".
The climate of New York (state) is generally humid continental, while the extreme southeastern portion of the state lies in the warmer humid subtropical climate zone. Winter temperatures average below freezing during January and February in much of the state of New York, but several degrees above freezing along the Atlantic coastline, including New York City.
Global weather activity of 2007 profiles the major worldwide weather events, including blizzards, ice storms, tornadoes, tropical cyclones, and other weather events, from January 1, 2007, to December 31, 2007. Winter storms are events in which the dominant varieties of precipitation are formed during cold temperatures; they include snow or sleet, or a rainstorm where ground temperatures are cold enough to allow ice, including freezing rain, to form. Thehy may be marked by strong wind, thunder, lightning thunderstorms, heavy precipitation, including ice storm, wind transporting some substance through the atmosphere, including dust storms, snowstorms, and hail storms. Other major non winter events such as large dust storms, hurricanes, cyclones, tornados, gales, flooding, and rainstorms are also caused by such phenomena.
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 Southeastern United States and the Northeastern United States in mid-February. Most of the cold weather abated by the end of March, though a few winter storms did affect the Western United States towards the end of the winter.
The 2014–15 North American winter was frigid and prolifically wintry, especially across the eastern half of North America in the months of January–March. The season began early, with many places in North America experiencing their first wintry weather during mid-November. A period of below-average temperatures affected much of the contiguous United States, and several records were broken. An early trace of snowfall was recorded in Arkansas. There were greater accumulations of snow across parts of Oklahoma as well. A quasi-permanent phenomenon referred to as the polar vortex may have been partly responsible for the cold weather. Temperatures in much of the United States dropped 15 to 35 °F below average by November 19, following a southward "dip" of the polar vortex into the eastern two-thirds of the country. The effects of this dip were widespread, bringing about temperatures as low as 28 °F (−2 °C) in Pensacola, Florida. Following a significant snowstorm there, Buffalo, New York received several feet of snow from November 17–21. In addition, significant winter weather occurred throughout the season, including a major blizzard that struck the Northeastern United States at the end of January, another blizzard that affected much of the Northern United States days later in early February, and several significant snow events paired with very frigid temperatures for much of February.
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 Northeastern United States, 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 United States, and the most notable event occurring in early February, when a powerful blizzard struck the Northeast and brought record snow to some areas. During the winter, a weak El Nino was expected to influence weather conditions across the continent.
The 2011–12 North American winter by and large saw above normal average temperatures across North America, with the Contiguous United States encountering its fourth-warmest winter on record, along with an unusually low number of significant winter precipitation events. The primary outlier was Alaska, parts of which experienced their coldest January on record.