National Weather Service Releases Winter Forecast

October 22, 2011; 4:10 AM ET
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The National Oceanic and Atmospheric Administration (NOAA) released its winter forecast. The following is NOAA's prediction, on par with AccuWeather.com's Winter 2011-2012 Forecast...

The southern Plains should prepare for weather that is drier and warmer than average to continue, while the Pacific Northwest is likely to be colder and wetter than average from December through February, according to the annual Winter Outlook released today by NOAA.

For the second winter in a row, La Niña will influence weather patterns across the country, but as usual, it's not the only climate factor at play. The 'wild card' is the lesser-known and less predictable Arctic Oscillation that could produce dramatic short-term swings in temperatures this winter.

NOAA expects La Niña, which returned in August, to gradually strengthen and continue through the upcoming winter. It is associated with cooler-than-normal water temperatures in the tropical Pacific Ocean and influences weather throughout the world.

"The evolving La Niña will shape this winter," said Mike Halpert, deputy director of NOAA's Climate Prediction Center. "There is a wild card, though. The erratic Arctic Oscillation can generate strong shifts in the climate patterns that could overwhelm or amplify La Niña's typical impacts."

The Arctic Oscillation is always present and fluctuates between positive and negative phases. The negative phase of the Arctic Oscillation pushes cold air into the U.S. from Canada. The Arctic Oscillation went strongly negative at times during the last two winters, causing outbreaks of cold and snowy conditions in the U.S. such as the "Snowmageddon" storm of 2009. Strong Arctic Oscillation episodes typically last a few weeks and are difficult to predict more than one to two weeks in advance.

Winter Outlook Precipitation

With La Niña in place, Texas, Oklahoma, New Mexico and parts of surrounding states are unlikely to get enough rain to alleviate the ongoing drought. Texas, the epicenter of the drought, experienced its driest 12-month period on record from October 2010 through September 2011.

Stormy periods can occur anytime during the winter season. To improve the ability to predict and track winter storms, NOAA implemented a more accurate weather forecast model on Oct. 18. Data gathered from the model will support local weather forecast office efforts to prepare for and protect the public from weather events. This service is helping the country to become a weather-ready nation at a time when extreme weather is on the rise.

Highlights of the U.S. Winter Outlook (December through February) include:

* 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 is 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 southern Atlantic Coast: drier than average, with an equal chance for temperatures that are above, near or below normal. Above-normal wildfire conditions.

* Ohio and Tennessee valleys: wetter than average with equal chances for temperatures that are above, near or below average. Potential for increased storminess and flooding.

* Northeast and mid-Atlantic: equal chances for precipitation and temperatures that are above, near or below normal. 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 into the Northeast could get 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 for precipitation that is above, near or below average. Statewide, the current drought is expected to continue through the winter. Drought recovery is more likely on 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 for the interior eastern part of the state.

This season's outlook does not project where and when snowstorms may hit or provide total seasonal snowfall accumulations. Snow forecasts are dependent upon winter storms, which are generally not predictable more than a week in advance.

Read the AccuWeather.com Winter 2011-2012 Forecast for more details on each region.

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