2017–18 North American winter

2017–18 North American winter
Seasonal boundaries
Meteorological winter	December 1 – February 28
Astronomical winter	December 21 – March 20
Seasonal statistics
Total fatalities	Unknown
Total damage	Unknown

The 2017–18 North American winter refers to winter in North America across the continent from late 2017 through early 2018. 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 will occur on March 20. Based on the meteorological definition, the first day of winter is December 1 and the last day February 28. Both definitions involve a period of approximately three months, with some variability.

Seasonal forecasts

Temperature Outlook

Precipitation Outlook

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 month of November began 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.

Events

Veterans' Day 2017 Cold Wave (November 9-13, 2017)

A strong Arctic front, which was caused by a displacement of the Polar vortex in the form of a stratospheric warming event over the North Pole, resulted in a number of record lows for the Midwestern and Northeastern United States. This came back as a shock to people that had yet to seen temperatures cold enough for frost, especially in New England. Before then, not only it was one of the warmest Fall seasons to that date, places like Philadelphia and Washington D.C. had yet to see a day/night that was below 40 °F (4 °C) since the previous Spring earlier that year. The low temperature early in the morning of November 11 was 23 °F (−5 °C). This came two degrees within reaching the record set for that day in 1961. Washington D.C. tied their record of 26 °F (−3 °C) that same morning set back in 1973. Forecasters even called for an earlier start to winter ahead of this cold wave.

Early December winter storm

File:December 2017 Winter Storm.png

The snowstorm on December 8 as it was affecting the U.S. Gulf Coast.

The December 8 snowstorm in Fairmount, Georgia

A strong winter storm affected areas from northeastern Mexico to the Northeastern United States in early December. The origins of the storm were complex, with the initial disturbance forming over the extreme southern United States as a stationary front left behind from a departing extratropical cyclone on December 7. At the same time, a cold airmass was establishing itself into the Deep South. A large plume of moisture encompassed the entire Gulf Coast, and snow broke out early on December 8 in places that rarely even see snow, including Mexico, southeastern Texas and Louisiana – even in the Florida Panhandle. The storm dropped up to 25 inches (64 cm) of snow in some parts of the Southeast as it slowly moved eastwards, breaking several snowfall records; meanwhile, a gulf low formed in the Gulf of Mexico the same day – this would ultimately become the dominant low of the system. Transitioning into an extratropical cyclone off the east coast of the United States, the system began moving parallel to the shoreline, with a large swath of snowfall accompanying it. The low slowly deepened throughout the day of December 9, bringing the first snow of the season to many parts of the Northeast and New England.

Up to 400,000 people were left without power across the affected regions, several schools and roads shut down, and 3 were have confirmed to have been killed by the storm as of December 9.

December 19-22, 2017 North American Snow and Ice Storm

In the third week of December, a cross-country snowstorm blanketed places between the Northwestern United States and New England. In New England, a serious ice storm brought up to 0.5 inches (1.3 cm) of ice accumulation in Shrewsbury, Massachusetts and 12.2 inches (31 cm) of snow in Moretown, Vermont. A ridge in the Southeastern United States helped steer the storm away from the Mid-Atlantic region. Several casualties were reported in the state of Massachusetts as a result.

December 23-25, 2017 North American Snowstorm

In the days leading up to Christmas, a snowstorm that formed in the Rockies on December 23 traversed through the Midwest on Christmas Eve. This resulted in a White Christmas for places in the Midwestern and Northeastern United States. It brought subtropical force winds, and brought snow rates in interior New England 3–5 inches (7.6–12.7 cm) per hour. Thundersnow was reported from eastern Massachusetts to eastern Maine. Overnight Christmas Eve, thundersnow was reported in Pittsburgh, Pennsylvania. The coastal low-pressure system rapidly intensified as it developed off the New England coast and moved northeastward into the Bay of Fundy. Snow at the rate of 1 inch per hour was reported Christmas morning in Bangor, Maine, Nashua, New Hampshire, Hartford, Connecticut, and Albany, New York, among other locations. Despite the fact that there was little or no accumulating snow in the Mid-Atlantic region, strong winds were felt. Even the heavy winds toppled a tree in Washington D.C. on 19th Street Northwest according to the National Weather Service.

Christmas Week 2017 Lake-Effect Snows

From Christmas Eve, December 24, until three days after, spanning a period of over 60 hours, a Lake-effect snow band that affected Erie, Pennsylvania, broke the state record for snow set in a single storm with 65.1 inches (165 cm), breaking the record that had been set in Morgantown, Pennsylvania, which previously set the Pennsylvania record snowfall in one storm after 50 inches (130 cm) as a result of the March 18-21, 1958 nor'easter. In addition, December 2017 was Erie's snowiest December on record, topping out the month with 102.1 inches (259 cm), breaking the old record of 66.9 inches (170 cm) in December 1989. Erie declared a snow emergency, stressing that roads were “dangerous and impassible.”

Late-December 2017 to Early-January 2018 North American Cold Wave

After Christmas Day, a strong Arctic airmass came and established from Canada into the Midwestern and Northeastern United States with the core of the cold centered in the Upper Midwest, Interior Northeast, and Eastern Canada. Temperatures were 10 to 20 °F (−12 to −7 °C) below average for that time of year. International Falls, Minnesota recorded a record low temperature on December 27 of −32 °F (−36 °C).

The ball drop on the evening of December 31 into the morning of January 1 at Times Square in the Manhattan section of New York City is expected to be one of the coldest ball drops on record at midnight. Temperatures are expected to be in the low teens at around midnight in Times Square.

External links

• 2017 Storm Summaries from the Weather Prediction Center