Harsh winter predicted

Thursday , August 16, 2012 - 11:34 AM

A man tries unsuccessfully to keep his car from sliding into another vehicle in Asheville, N.C. on...

Jason Samenow

After last year’s virtual snow shutout, AccuWeather predicts that the southern Mid-Atlantic to southern New England will get walloped in the coming winter.

In its winter outlook, released this week, AccuwWeather forecasts above-average snowfall for major Interstate 95 corridor cities, including Richmond, Washington, Baltimore, Philadelphia and New York.

The cities "could get hit pretty good," AccuWeather.com forecaster Paul Pastelok said. "It’s a matter of getting the cold to phase in with the huge systems that we are going to see coming out of the southern branch of the jet stream this year."

Our team of winter weather experts and long-range forecasters at The Post’s Capital Weather Gang suggests that AccuWeather’s forecast amounts to a speculative guess and is about as likely to be wrong as right.

The principal reason AccuWeather favors big Mid-Atlantic and I-95 snows is tied to its expectation of the development of a weak-to-moderate El Nino, the warm current that flows in the central to eastern Pacific Ocean along the equator.

A weak-to-moderate El Nino, it says, features "a strong southern branch of the jet stream across the U.S." that can join up with the northern branch of the jet stream and produce big East Coast snowstorms.

Matt Ross, lead author of our winter weather outlook, cautions that it’s too early to predict the strength of the El Nino. Furthermore, he doesn’t think a weak-to-moderate El Nino guarantees big snow even if it materializes.

"I believe a weaker event would not be as favorable for cold and snow in the D.C. area as AccuWeather is suggesting," Ross said.

Matt Rogers, who also specializes in long-range forecasting for the CWG, said it’s important to recognize that El Nino winters have produced widely varying snowfall totals in the region.

"There is an inconsistent history of El Nino and D.C. winter snow," he said.

Although Rogers agrees with AccuWeather’s prediction for a weak-to-moderate El Nino, he stressed other factors play a big role in mid-Atlantic snowfall.

"El Nino winters can supply significant winter snow to the East Coast if they are accompanied by bigger blocking patterns in the North Atlantic," he said.

The blocking patterns Rogers mentions help establish cold air over eastern North America - and keep it there - which is critical for big storms to produce snow rather than rain.

El Nino years historically average more snowfall (around 19 inches) than the 30-year average (14.5 inches) in D.C., CWG winter weather expert Wes Junker said. But after analyzing the data, he found only 50 percent of El Nino years since 1950 (20 seasons) have been snowier than normal.

Last year at this time, AccuWeather’s Henry Margusity predicted "near normal" snow along the I-95 corridor and above-normal snow in the mountains. Most of this region experienced much-below-normal snow.

Junker’s response to Margusity’s prediction at the time was: "I think it’s too early to make any definitive call about snow or even what the winter will be like."

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