Winter outlook: El Nino may mean stormy conditions in the South and Eastern U.S.

Washington Post

The past three winters have proved mild in the Eastern United States, and, in many places, snow has been scarce. This winter may be different, the National Oceanic and Atmospheric Administration announced Thursday in its annual winter outlook.

Because of a likely El Nino, which is the episodic warming of the eastern and central tropical Pacific Ocean, NOAA favors above average amounts of precipitation along the southern tier of the United States, creeping up the East Coast through the Mid-Atlantic.

"We find ourselves on the verge of El Nino," said Mike Halpert, deputy director of NOAA's Climate Prediction Center, on a call with reporters Thursday. "There's a 70-to-75 percent chance El Nino will develop in the next few months."

Historically, El Nino events have boosted precipitation amounts across the South and into the Mid-Atlantic and sometimes snowfall as well. In the Mid-Atlantic region, the amount of snow has depended on the strength of El Nino. Moderate and strong El Nino events have tilted the odds toward heavy snow in the Mid-Atlantic, but weak events have not.

Halpert said this El Nino is likely to be a weak one. The last time there was an El Nino event, in the winter of 2015-2016, the Mid-Atlantic was hit by a blockbuster snowstorm. That El nino event ranked among the strongest on record.

"We're expecting this El Nino to be much weaker than that one," Halpert said.

The prospect of stormy conditions in the Southeast and Mid-Atlantic means it has the greatest chance of having colder-than-normal conditions of anywhere in the country, Halpert said. Even so, the NOAA forecast indicates "equal chances" of above-, normal or below-normal temperatures in this zone.

Everywhere else across the nation is favored to be warmer than normal. The Pacific Northwest, in particular, has high odds of a mild winter.

"No part of the U.S. is favored to have below-average temperatures," Halpert said.

Matt Rogers, president of the Commodity Weather Group, which specializes in long-range prediction, agreed with the broad strokes of NOAA's outlook but said its temperature forecast was "conservative" in the East and that he would lean toward colder conditions. He said there is a chance El Nino could reach moderate strength and a "blob" of warm water setting up in the Northeast Pacific Ocean could set up a jet stream pattern that maximizes the delivery of cold air into the eastern United States.

If NOAA's outlook holds true and much of the nation is milder than normal, it will mark the fourth straight warmer-than-normal winter for the Lower 48.

Last winter ranked among the warmest third in historical records, 1.8 degrees above normal averaged over the nation. The warmest conditions were found in the Southwest.

Two winters ago was practically the winter without a winter. Spring arrived weeks ahead of time, and Chicago basked in record 70-degree warmth in February. It ranked as the sixth-warmest winter on record, and everywhere, except the Pacific Northwest, was warmer than normal.

The winter before that, 2015-2016, was the warmest on record for the Lower 48, despite the big snowstorm in the Mid-Atlantic.

While natural fluctuations play a significant role in the flavor of a given winter, the rising concentrations of greenhouse gases in the atmosphere is stacking the deck in favor of warm winters.

How confident should you be in this outlook?

Halpert said the track record of winter outlooks is better than that of outlooks for other seasons, or about 40 percent better than the flip of a coin - good enough for people to be able to utilize the outlooks.

Because of the uncertainty in seasonal prediction, NOAA's winter outlook is probabilistic in nature, meaning that a range of outcomes is possible in any area. That means, invariably, some areas will experience conditions opposite the most likely forecast even if most locations are correctly predicted, Halpert said.

First published in The Washington Post

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