From the ABC 7 Weather team

2011 U.S. winter outlook: dry South, cold North, D.C. unsure

October 21, 2011 - 05:00 AM
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La Niña dominates the U.S. again this winter, and the Arctic Oscillation could provoke big snows in the Northeast, according to NOAA.

NOAA's 2011 winter outlook calls for warmer and drier conditions in the South and colder and wetter ones in the Pacific Northwest. The Mid-Atlantic region could be whipped with temperature extremes caused by the Arctic Oscillation. (Pictured: The temperature outlook for Dec. 2011 to Feb. 2012)

D.C. residents, brace yourself for a wallop of shocking information: There are "equal chances for above-, near-, or below-normal temperatures and precipitation" in the Mid-Atlantic this winter, according to an analysis by NOAA's Climate Prediction Center. (Press release, full outlook here.)

That's not very helpful for people wondering how many snow shovels to buy from the hardware store this November. (The answer is five.) But don't blame the forecasters too much. The D.C. region is in a weird geographic slot that makes it tough to predict the conditions from December to February.

The big climate player this year is La Niña, the mild-mannered sister of El Niño that is associated with below-average temperatures in the Pacific Ocean. Winters under the spell of La Niña (last year was one) typically feature hotter-than-usual temperatures in the Southeast U.S. and cooler-than-average temperatures in the Northwest.

And that's roughly what NOAA's analysis predicts. Signs of La Niña's reappearance started appearing in August, and the government meteorologists see it building in strength through the frigid months ahead. That would mean better chances of warmer and drier weather in the South, a foreboding thought for farmers whose drought-stricken land isn't growing squat. It would also ratchet up the winter damp and chill in the Flannel Belt running through Washington State, Oregon and some of the northern states.

This is how NOAA sees the precipitation spreading out in the coming months:

us winter outlook 2011 2012 precipitation

La Niña doesn't do so much for the Mid-Atlantic in winter. This region instead falls under the influence of a pattern of dueling northern pressure zones called the Arctic Oscillation. When the oscillation goes from positive to negative – meaning high pressure dominates the pole while low pressure swirls south around the mid-latitudes – it can push tons of freezing air over the East Coast and cause, in one famous instance, a Snowmageddon. But these periodic switches of the oscillation are incredibly hard to predict. So NOAA is hedging its winter forecast with this language: "If enough cold air and moisture are in place, areas north of the Ohio Valley and into the Northeast could see above-average snow."

In other words, we'll just have to wait a while to see which direction the weather is heading. For a full list of the expected effects of the 2011/2012 winter around the country, plow ahead. You may also want to check out an earlier winter prognosis released by WSI, a company owned by the Weather Channel.

NOAA's outlook predicts:

* 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.

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