The Pacific Northwest should brace for a colder and wetter than average winter, while most of the South and Southeast will be warmer and drier than average through February 2011, according to the annual Winter Outlook released today by NOAA’s Climate Prediction Center. A moderate to strong La Niña will be the dominant climate factor influencing weather across most of the U.S. this winter.

La Niña is associated with cooler-than-normal water temperatures in the Equatorial Pacific Ocean, unlike El Niño, which is associated with warmer than normal water temperatures. Both of these climate phenomena, which typically occur every two to five years, influence weather patterns throughout the world and often lead to extreme weather events. Last winter’s El Niño contributed to record-breaking rain and snowfall leading to severe flooding in some parts of the country, with record heat and drought in other parts of the country. Although La Niña is the opposite of El Niño, it also has the potential to bring weather extremes to parts of the nation.

“La Niñais in place and will strengthen and persist through the winter months, giving us a better understanding of what to expect between December and February,” says Mike Halpert, deputy director of the Climate Prediction Center – a division of the National Weather Service. “This is a good time for people to review the outlook and begin preparing for what winter may have in store.”

“Other climate factors will play a role in the winter weather at times across the country,” added Halpert. “Some of these factors, such as the North Atlantic Oscillation, are difficult to predict more than one to two weeks in advance. The NAO adds uncertainty to the forecast in the Northeast and Mid-Atlantic portions of the country.”

Regional highlights

Regional highlights include:

California and the Southwest: Warmer and drier than average. This will likely exacerbate drought conditions in these areas. All southern states are at risk of having above normal wildfire conditions starting this winter and lasting into the spring.

Northern Plains: Colder and wetter than average. Likely to see increased storminess and flooding.

Southern Plains, Gulf Coast States & Southeast: Warmer and drier than average. This will likely exacerbate drought conditions in these areas. All southern states are at risk of having above normal wildfire conditions starting this winter and lasting into the spring.

Ohio and Tennessee Valleys: Warmer and wetter than average. Likely to see 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 weather patterns over the northern Atlantic Ocean and Arctic. These are often more short term, and are generally predictable only a week or so in advance. If enough cold air and moisture are in place, areas north of the Ohio Valley and into the Northeast could see above-average snow.

Central U.S.: Equal chances of above-, near- or below-normal temperatures and precipitation;

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

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