The 2017–18 North American winter saw weather patterns across North America that were very active, erratic, and protracted, especially near the end of the season, resulting in widespread snow and cold across the continent during the winter. Significant events included rare snowfall in the South, an outbreak of frigid temperatures that affected the United States during the final week of 2017 and early weeks of January, and a series of strong nor'easters that affected the Northeastern United States during the month of March. In addition, flooding also took place during the month of February in the Central United States. Finally the winter came to a conclusion with a powerful storm system that caused a tornado outbreak and blizzard in mid-April. The most intense event, however, was an extremely powerful cyclonic blizzard that impacted the Northeastern United States in the first week of 2018. Similar to the previous winter, a La Niña was expected to influence the winter weather across North America.
While there is no well-agreed-upon date used to indicate the start of winter in the Northern Hemisphere, there are two definitions of winter which may be used. Based on the astronomical definition, winter began at the winter solstice, which in 2017 occurred on December 21, and ends at the March equinox, which in 2018 occurred on March 20. Based on the meteorological definition, the first day of winter is December 1 and the last day February 28. Each definition involves a period of approximately three months, with some variability with both definitions containing two months and a week. Winter is often defined by meteorologists to be the three calendar months with the lowest average temperatures. Since both definitions span the calendar year, it is possible to have a winter storm in two different years.
Seasonal forecasts
On October 19, 2017, the National Oceanic and Atmospheric Administration's Climate Prediction Center released its U.S. Winter Outlook. The outlook noted a 55–65% chance that a La Niña would develop. According to CPC Deputy Director Mike Halpert, any such La Niña was expected to be "weak and potentially short-lived", but it could still affect the season. He also noted that La Niña years normally result in colder-than-average, wetter winters in the northern tier of the United States and the inverse conditions across the south. In terms of precipitation, wetter-than-average conditions were favored across the majority of the northern United States, including a region spanning from the northern Rocky Mountains to the eastern Great Lakes in addition to the Ohio Valley, Hawaii, and western and northern Alaska. Drier conditions were anticipated across the entire southern United States.
Above-average temperatures were favored across the southern two-thirds of the contiguous United States and along the east coast, as well as in Hawaii and the northern and western parts of Alaska. The outlook favored below-average temperatures in the northern tier, from Minnesota to the Pacific Northwest region as well as southeastern Alaska.
The remainder of the country was assigned equal chances of either above or below-normal temperatures or precipitation. The drought outlook noted that drought was likely to remain in parts of the northern Plains, with recovery likely to the west. The development of limited regions of drought was possible in regions that did not receive rainfall associated with tropical systems during the 2017 Atlantic hurricane season.
Seasonal summary
The North American winter of 2017–18 began in the month of November with the highest snow extent in at least one and a half decades, with snow covering over a quarter of the contiguous United States, 22% more than the same date in 2011, the next-most-recent year with comparable snow coverage at that date. However, this trend did not last through all of the month, with the last week having the least snowfall of that time of year for the same time period. This extensive snowpack was due in part to cold temperatures on an extent not seen since at least 2014 in the early part of the month caused by an Arctic front advancing southward into the northern United States, breaking several record low temperatures in major cities from the Upper Midwest to the Mid-Atlantic. In Minnesota, at least several places recorded temperatures below on November 10, breaking several record lows – some places reached as low as . In early December, following another outbreak of cold temperatures, a major winter storm impacted the far southern reaches of the United States – areas as far as the southern portions of the Gulf Coast up to the Mid-Atlantic states and New England received a wide swath of accumulating snowfall, significantly hampering travel and knocking power out to tens of thousands.Southern Plains to Northeast Winter Storm 7-10 December, 2017. WPC The rest of the month was generally warmer than average nationwide, primarily in the southwestern United States, and ranked as the third-warmest in historical records. However, towards the end of the month, an outbreak of below-average temperatures impacted much of the continental United States over the holiday, with New York City recording its second-coldest New Year's Eve on record with a temperature of .
January and the new year opened with cold temperatures remaining in place across the eastern part of the country, which would continue until the middle of the month. In the first week of 2018, an extremely powerful cyclonic blizzard developed off the Southeastern United States, explosively deepening as it traveled parallel to the East Coast.Eastern United States Winter Storm 03-05 January, 2018. WPC The blizzard delivered snow as far south as Florida which rarely sees snowfall at all, and left a wide swath of snowfall totals up to in the Mid-Atlantic and New England. In addition, major coastal flooding occurred with the system as well and killed at least 11 people. The following week around January 12–13, a major winter storm affected much of the Appalachian Mountains and interior New England, and a few days later on January 16, a separate system dumped as much as in areas of North Carolina, and for the second time in a month brought snowfall to areas of the Florida Panhandle.Southern and Eastern U.S. Snowfall January 16-18, 2018. WPC Another winter storm brought blizzard-like conditions and up to a foot of snow in the Upper Midwest the following week, with the Twin Cities in Minnesota receiving their largest one-day snowfall since December 2010 with falling on January 22. The long-term pattern that brought below-average temperatures to the eastern half of the United States largely abated by the latter part of January, but not before causing drought conditions to expand within the West to its largest coverage since May 2014, due to above-average temperatures across much of the region. The end of January saw some scattered snow-related events, but a pattern change in February brought warmer conditions to most of the U.S., and thus few wintry weather events – except for one that struck the Northeast in mid-February. Unprecedented warmth days later sent temperatures as high as on February 21 in the eastern half of the country.Record warmth in February 2018. Climate.gov. March 6, 2018
By the turn of March, however, a major pattern shift occurred in which the same regions in the Northeast were hit by four consecutive rounds of nor'easters and heavy snow within a three-week period. This led places such as New York City and New Jersey to have a March that was cooler then the previous February.March 2018 Weather Recap: Chronic Chill Follows Mildest February, TypePadThe Lion Roared All Month Long: March 2018 Summary, NJWeather, April 7, 2018 The first one developed on March 1, and although the most severe damage was caused by flooding as well as snow, unusually high tides and storm surges along the coast, wind and downed trees caused massive inland power outages, Days later, a second nor'easter developed and rapidly strengthened while bringing heavy snowfall to New Jersey and interior New York. The storm caused up to 1 million people to lose power. Hundreds of flights were cancelled across the region, and many schools closed due to the nor'easter. Several municipalities in the Philadelphia area declared snow emergencies and many schools and government offices were closed on March 7. Nearly a week later, a third nor'easter affected the New England coast with near-blizzard conditions and coastal flooding on March 13. Wind gusts of were reported at Logan International Airport in Boston while gusts reached on Nantucket Island, in Hyannis, and in East Falmouth. A storm surge of was reported on Nantucket while a storm surge was recorded in Boston. Over a foot of snow was reported in portions of New Hampshire, with Deefield receiving almost 29 inches and Middleton reported 28 inches. No widespread power outages were reported. The storm brought heavy snow and blizzard conditions to Maine on March 13. Blizzard conditions were reported in Portland. Over a foot of snow was reported in portions of the state. The fourth and final nor'easter occurred on March 20 to 22, with its focus further south in the Mid-Atlantic. Some areas saw their heaviest late-season snowfall on record, and approximately 100,000 lost power as a result of the storm. The pattern largely abated by late March, but soon made a comeback as many regions in the northern half had one of the coldest Aprils on record, and the snowpack in the U.S. was well-above average for the month of April. Part of this was due to a rare, late-season and powerful blizzard that struck the High Plains with nearly of snowfall. Wintry weather soon came to an end in the country for the season after the storm had passed.
Events Late October nor'easter
Near the end of October, just before Halloween, a powerful extratropical cyclone formed in the Atlantic Ocean off of the coast of New England. Rapidly intensifying into a powerful nor'easter, the winter storm was enhanced by moisture left over from Tropical Storm Philippe – which dissipated over Cuba and spawned an unrelated non-tropical low that the nor'easter later absorbed – before hitting New England and eastern Canada.
The nor'easter resulted in approximately 1.2 million power outages in New England. The system produced tropical storm-force sustained winds, reaching 57 mph (92 km/h) in Warwick, Rhode Island, and hurricane-force wind gusts, peaking at 93 mph (150 km/h) in Popponesset, Massachusetts. The system also produced snowfall mainly in the higher elevations, in areas such as West Virginia and some parts of western Maryland. Snowfall totals reached up to over in some spots, causing accidents and requiring snow plowers to be deployed in Preston County.
In Canada, Hydro-Québec reported 200,000 customers losing power because of damages due to winds of . It also rained heavily in Quebec and Eastern Ontario, with up to in the Canadian capital region of Ottawa forcing Prime Minister Justin Trudeau to use an all-terrain vehicle to leave from his second home on Mousseau Lake in Gatineau Park to go to Parliament.
Mid-November cold wave