“With La Niña well established and expected to persist through the upcoming 2020 winter season, we anticipate the typical, cooler, wetter North, and warmer, drier South, as the most likely outcome of winter weather that the U.S. will experience this year,” said Mike Halpert, deputy director of NOAA’s Climate Prediction Center, in a news release.
In a call with reporters, Halpert said La Niñas reduce the odds of big East Coast snowstorms, but that such extreme events cannot be predicted months in advance, according to the Associated Press.
Severe outbreaks of Arctic air are common during La Niñas, but the core of the cold typically focuses in the northern Rockies, Plains and Upper Midwest, and substantially moderates by the time it reaches the East Coast.
Because La Niñas tend to shut down the transport of moisture from the tropical Pacific into Southern California, NOAA’s outlook calls for drought to intensify and expand from the Southwest to the Southern Plains. This zone includes areas where wildfires currently rage, such as Southern California and Colorado.
NOAA’s temperature outlook calls for the highest chance of warmer-than-average winter weather from Arizona to Florida. Somewhat lesser odds of milder-than-average weather span from northern California to western Pennsylvania to New York. In between, elevated chances for a mild winter stretch from the southern part of the West Coast to the Mid-Atlantic and Northeast.
The only region where colder-than-average weather is favored spans from the Pacific Northwest to the northern Plains. Just to the south of this zone, which includes much of the Upper Midwest, NOAA assigns equal chances of a mild or cold winter.
NOAA leans toward drier-than-average conditions from central California to the Virginia Tidewater and North Carolina Outer Banks and everywhere to the south. It assigns particularly high odds of dry conditions from southern Arizona to Florida.
It favors wetter-than-average conditions from the Pacific Northwest to the Ohio Valley, with the highest odds from eastern Washington to northwest Minnesota, and in Michigan, Indiana and western Ohio. Storm tracks during La Niña events tend to favor the most action along the northern tier. Although NOAA does not issue a snowfall outlook, above-average amounts in this zone can be inferred.
NOAA’s outlook similar to others
NOAA’s temperature outlook is similar to ideas presented by the Weather Company and AccuWeather, two of the larger private companies issuing winter projections.
The outlook from the Weather Company, owned by IBM, calls for above-average temperatures over much of the nation except for parts of Montana and North Dakota. However, Todd Crawford, its chief meteorologist, wrote La Niñas can have “significant volatility” depending on the configuration of weather systems at high latitudes.
When zones of “blocking” high pressure develop in places such as Greenland, it can force the jet stream to plunge south over the Eastern U.S., resulting in cold, stormy conditions. Such blocking events can override the effects of La Niña, the Weather Company’s outlook stated.
The outlook from AccuWeather, based in State College, Pa., also favors milder-than-average conditions over much of the Lower 48, except for the northern Rockies and parts of the Pacific Northwest.
Like the Weather Company, it also sees the potential for big swings in weather.
“The entire season will not be mild all the way through,” its outlook for the Northeast and Midwest states. “Instead, the season will be bookended by cold and snowy conditions with a pause in the wintry weather in the middle of the season.”
The swings may be particularly sharp in the Plains and the Rocky Mountains, AccuWeather noted. “Periods of subzero cold can drive south down the Front Range of the Rockies, the central and western Plains,” wrote its lead forecaster, Paul Pastelok.
The mild weather predicted from the Mid-Atlantic to the Southeast will shut down snowfall there, AccuWeather predicts, but amounts should increase to the Northwest.
Overall, AccuWeather’s outlook forecasts near- to above-average snow in the northern Rockies and Upper Midwest and near- to below-average snow for much of the Northeast and Ohio Valley.
AccuWeather’s snowfall outlook is not dissimilar from projections from European and United Kingdom computer modeling, which also suggest below-normal amounts in the East and South and above-normal totals to the North and West across the Lower 48:
Seasonal outlooks do not have the same degree of accuracy and reliability as day-to-day weather forecasts. NOAA’s winter temperature outlooks, for example, typically provide a 30 to 35 percent improvement over a random guess, while precipitation outlooks offer only about half that much improvement.
NOAA’s 2019-2020 winter outlook was considered a success, but its outlook the year before predicted essentially the opposite of what occurred.