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2019–20 North American winter

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  • 4 chapters

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Through El Niño–Southern Oscillation, Montreal and Mississippi

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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 begins at the winter solstice, which in 2019 occurred on December 21, and ends at the March equinox, which in 2020 occurred on March 19. Based on the meteorological definition, the first day of winter is December 1 and the last day February 29. Both definitions involve a period of approximately three months, with some variability. 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 spanning two different years.

Seasonal forecasts

On October 17, 2019, the National Oceanic and Atmospheric Administration's Climate Prediction Center released its U.S. Winter Outlook. The El Niño–Southern Oscillation was in its neutral phase and was thus not expected to be a key predictor for the season. As a result, other oscillations such as the Madden–Julian Oscillation and the Arctic Oscillation were anticipated to be more significant drivers of the seasonal weather, particularly in the form of large temperature and precipitation swings. From the outlook, the greatest likelihoods for above-normal temperatures were for Alaska and Hawaii, with lower but still above-normal odds of above-average temperatures for most of the lower 48 states. The exception was for the Northern Plains, Upper Mississippi Valley, and western Great Lakes regions, which were ascribed equal changes for above-, near-, or below-average temperatures. No area in the United States was favored to have below-average temperatures. In terms of precipitation, wetter-than-average conditions were most likely in Alaska, Hawaii, part of the Northern Plains, Upper Mississippi Valley, Great Lakes, and parts of the Mid-Atlantic and Northeastern U.S. Drier-than-average conditions were favored for Louisiana and parts of Texas, Mississippi, Arkansas, and Oklahoma, as well as parts of central and northern California, with the rest of the U.S. having equal changes of above-, near-, or below-average precipitation. The drought outlook highlighted the presence of abnormally dry conditions across much of the Southern U.S, with improvement expected in part of the Southeast and Mid-Atlantic regions, Alaska, and Hawaii. Drought was expected to persist in central Texas and the Southwestern U.S, with further development anticipated in parts of central California.

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