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Posted at 12:56 PM ET, 10/20/2011

NOAA winter outlook: Drought to deepen in Texas; cold and stormy across northern U.S.


NOAA’s winter temperature outlook. (NOAA)
Suffering its worst drought on record, dry, warm conditions are predicted to persist through winter across Texas according to NOAA’s winter outlook, released this morning. The outlook is based on the redevelopment of La Nina, an episodic cooling of the tropical Pacific ocean, which often brings warmer and drier than average conditions across the southern U.S., and cold, stormy conditions across the northern tier.

But for much of the East Coast, NOAA assigned equal chances of a cold or warm winter and a wet or dry winter . It stopped short of making a definitive forecast due to the lack of predictability of the phase of the Arctic Oscillation (AO) which often dictates how cold or wet it is along the East Coast.


NOAA’s winter precipitation outlook. (NOAA)
When the AO is negative, cold air pours out of Canada into the eastern two-thirds of the U.S. A negative AO is also often conducive to stormy, snowy conditions. The AO was highly negative during the record snowy winter in 2009-2010 in the mid-Atlantic.

“The Arctic Oscillation is the fly in the ointment,” said Mike Halpert, deputy director of NOAA’s Climate Prediction Center. “That’s why the temperature forecast has equal chances along the East Coast.”

“We don’t have the tools at this point to make a forecast on the Arctic Oscillation, ” Halpert said.

Recent research from climate researcher Judah Cohen, at Atmospheric and Environmental Research, has drawn connections between fall Siberian snow cover and the phase of the AO. But Halpert is unconvinced this snow cover indicator can fully predict what the AO is going to do.

“Maybe Siberian snow cover plays some role, but is not the entire answer,” said Halpert. “Maybe someday we’ll be able to unlock that mystery.”

While cautioning the AO could overwhelm or intensify La Nina’s effects, NOAA was clear that the developing La Nina served as the basis for its outlook. “The evolving La Niña will shape this winter,” said Halpert.

La Nina was a major driver of last winter’s weather when the drought became established in Texas and began to spread into the southern Plains. David Brown, NOAA’s regional climate services director for its Southern Region, said extreme to exceptional drought now covers 91% of Texas, 87% of Oklahoma, and 63% of New Mexico. The economic toll from the drought has reached $5 billion in Texas and $1.5 billion in Oklahoma.

Last year’s La Nina also supported cold, snowy winters in northern cities like Minneapolis, Chicago, New York and Boston.

After waning in the spring, La Nina redeveloped this summer. At present, the La Nina is a weak one with sea surface temeperatures 1 to 2 degrees F below average in the Pacific. But Halpert said there’s some potential for La Nina to “gradually strengthen.”

In addition to favoring the persistence of drought conditions in the Southern Plains, NOAA cautioned La Nina conditions may result in drought spreading to parts of the Gulf Coast and Florida.

NOAA’s outlook for a dry, warm conditions in the south (compared to normal) and cold and stormy conditions in the north is similar to AccuWeather’s winter predictions released two weeks ago.

Here are highlights of NOAA’s winter outlook, reproduced from its website:

* Pacific Northwest: colder and wetter than average. La Niña often results in below-average temperatures and increased mountain snow in the Pacific Northwest and western Montana during the winter months. This may set the stage for spring flooding in the Missouri River Basin;

* California: colder than average with odds favoring wetter than average conditions in northern California and drier than average conditions in southern California. All of the southern part of the nation are at risk of having above normal wildfire conditions starting this winter and lasting into the spring;

* Northern Plains: colder and wetter than average. Spring flooding could be a concern in parts of this region;

* Southern Plains and Gulf Coast States: warmer and drier than average. This will likely exacerbate drought conditions in these regions;

* Florida and south Atlantic Coast: drier than average, with an equal chance for above-, near-, or below-normal temperatures. Above normal wildfire conditions;

* Ohio and Tennessee Valleys: wetter than average with equal chances for above-, near-, or below-average temperatures. Potential for increased storminess and flooding;

* Northeast and Mid-Atlantic: equal chances for above-, near-, or below-normal temperatures and precipitation. 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;

* Great Lakes: tilt toward colder and wetter than average;

* Hawaii: Above-average temperatures are favored in the western islands with equal chances of above-, near-, or below average average precipitation. Statewide, the current drought is expected to continue through the winter. Drought recovery is more likely over the windward slopes of the Big Island and Maui;

* Alaska: colder than average over the southern half of the state and the panhandle with below average precipitation in the interior eastern part of the state

By  |  12:56 PM ET, 10/20/2011

Categories:  Latest, U.S. Weather

 
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