La Nina Strikes Again! NOAA: Colder, Wetter North; Drier South; 'Snowmaggeddon' Threat in East

Matt Cover | October 20, 2011 | 1:58pm EDT
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U.S. Winter Outlook (NOAA)

( - The National Oceanic and Atmospheric Administration (NOAA) predicted Thursday that La Nina and the Arctic Oscillation would bring a colder and wetter winter season to the Northwest and central regions of the country--and potentially another ‘Snowmaggeddon’ to the Northeast and Mid-Atlantic.

At the same time, NOAA is predicting below average precipitation across the southern United States, with "severe drought" continuing through the winter across the Southern Plains.

Precipitation, NOAA predicts, will be as much as 50 percent below the median in the southern parts of Arizona, New Mexico, and Oklahoma, and through much of drought-plagued Texas. In some other parts of those states, as well as in parts of Southern California, Louisiana, Alabama, Georgia, South Carolina and North Carolina, winter precipitation will be as much as 40 percent below the median, according to NOAA.

Additionally, NOAA expects drought conditions to spread to Florida, where winter precipitation this year will be as much as 40 to 50 percent below the median.

By contrast, NOAA is predicting that winter precipitation could be as much as 50 percent above the median in the Northwest and from 33 percent to 40 percent above the median in parts of the Midwest.

“The winter outlook this year is shaped by the redevelopment of La Nina,” Mike Halpert, deputy director of NOAA’s Climate Prediction Center said on a conference call with reporters.

NOAA defines La Nina as “unusually cold ocean temperatures in the Equatorial Pacific.”

“In very general terms,” NOAA’s Halpert said, “the outlook favors colder, and wetter than average conditions along the northern part of the nation from the Pacific Northwest to the Great Lakes and drier and warmer than average conditions across much of the South, particularly in the southern Plains.

“More specifically,” he said, “a colder than average winter is most likely right along the West Coast and across the northern Plains and Great Lakes states, while a milder than average winter is favored across the south central part of the nation, from the Southwest eastward across the southern Plains to the central Gulf Coast.”

NOAA said that precipitation would be heavier than usual in the northern parts of the country and down the valleys of the Ohio and Tennessee rivers.

“Winter-time precipitation and potentially snowfall is most likely to exceed median values across much of the northern part of the nation from the Pacific Northwest across the central and northern Rockies, the northern Plains and Great Lakes, and southward into the Ohio and Tennessee River valleys,” Halpert said.

NOAA also aid that an atmospheric effect known as the Arctic Oscillation could intensify the winter in the East by bringing colder temperatures, thus causing heavier snowfalls reminiscent of the “Snowmaggedon” storm that have hit the region in 2009.

Explaining that the intensity of the coming winter will be determined not by La Nina alone or by the Arctic Oscillation alone, but by the intensity and interaction of the two phenomena, Halpert said, “It is important to note however that the strength of U.S. impacts is not directly related to the strength of La Nina.”

In the Northeast and Mid-Atlantic states the primary factor will be the Arctic Oscillation.

“The negative phase of the Arctic Oscillation pushes cold air into the U.S. from Canada,” said a NOAA press statement. “The Arctic Oscillation went strongly negative at times the last two winters, causing outbreaks of cold and snowy conditions in the U.S. such as the ‘Snowmaggedon’ storm of 2009.”

NOAA said that if the Arctic Oscillation pushes cold air into the United States, the Northeast and Mid-Atlantic could see heavy snows again this year.

“Winter weather for these regions is often driven not by La Niña but by the Arctic Oscillation. If enough cold air and moisture are in place, areas north of the Ohio Valley and into the Northeast could see above-average snow,” the NOAA press release explained.

This could happen, NOAA is predicting, even as other parts of the country remain in severe drought.

"Despite the recent rains, ongoing extreme drought continues throughout the southern Plains, and it's most likely that severe drought will persist through the winter," NOAA's Halpert said. "In addition, we expect drought to develop during the winter throughout some parts of the Southeast not currently experiencing drought, including much of Florida."

David Brown, NOAA Regional Climate Services Director for the Southern Region, said that 91 percent of Texas was under "extreme drought" or "exceptional drought" conditions.

Brown added that as the drought conditions spread into Florida and other parts of the Southeast, the chance of wildfires would increase for those areas as groundwater levels continue to decline.

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