Two different views of the oncoming 2017-18 winter season are making their way into discussion this week.
The National Oceanic and Atmospheric Administration (NOAA) announced its winter forecast Oct. 19. The NOAA forecast noted that the Pacific Ocean temperatures are likely to fall to La Nina levels during the rest of calendar year 2017, with a 55% to 65% chance of La Nina developing and being in effect through winter.
“Typical La Nina patterns during winter include above-average precipitation and colder-than-average temperatures along the northern tier of the U.S. and below-normal precipitation and drier conditions across the South,” said NOAA Climate Prediction Center Deputy Director Mike Halpert in a news release.
NOAA’s U.S. winter precipitation forecast (December, January, February) calls for above-average amounts in the northern U.S., from the northern Rockies to the Great Lakes and Ohio Valley. Drier-than-normal conditions are indicated across the entire southern U.S.
NOAA’s forecast also calls for warmer-than-normal conditions over the southern two-thirds of the U.S. and the entire East Coast. Below-average temperatures are favored along the northern tier of the contiguous U.S., from Minnesota to the Pacific Northwest. The rest of the country falls into an “equal chance” category for either above-, near- or below-normal temperatures.
The NOAA forecast wasn’t the only forecast that has been posted, however. Private weather company forecasts are also being shared, and there are some differences with the public outlook, especially on temperatures.
DTN’s winter weather outlook has a broader expanse of colder-than-normal conditions than the NOAA forecast is indicating, with the influence of the polar vortex from the Arctic latitudes more pronounced, and adding to the impact of La Nina.
“There will be greater, periodic risks for Arctic cold when the polar vortex is displaced southward,” DTN forecaster Jeff Johnson noted in prepared remarks for a winter outlook webinar.
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DTN’s winter temperature forecast calls for a large portion of the north-central and northeastern U.S. — instead of an “equal chance” temperature trend — to have more cold periods during the ’17-18 winter season. DTN’s forecast also has the potential for an “extended winter” in the Midwest, meaning lower temperatures could linger into calendar year 2018.
Along with that colder air, “snowfall will be heavier than average in the Northwest, Upper Midwest, Great Lakes and Ohio Valley,” the DTN presentation highlighted. The DTN forecast also calls for heavier precipitation in the Tennessee Valley region.
The NOAA outlook summary comments also noted the potential for the polar vortex influence to affect the winter 2017-18 weather pattern. However, such an event “is difficult to predict more than one to two weeks in advance,” said Halpert.
Bryce Anderson can be reached at email@example.com
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