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U.S. will see weather extremes this winter

A moderate to strong La Niña will be the dominant climate factor influencing weather throughout most of the U.S. this winter, according to the annual Winter Outlook released by the National Oceanic and Atmospheric Administration's (NOAA's) Climate Prediction Center.

La Niña is associated with cooler than normal water temperatures in the Equatorial Pacific Ocean, and El Niño is associated with warmer than normal water temperatures. These climate phenomena, which typically occur every two to five years, influence weather patterns throughout the world and often lead to extreme weather events.

In 2009, El Niño contributed to record-breaking rain and snowfall leading to severe flooding in some parts of the U.S., as well as record heat and drought in other parts of the country. This winter, La Niña has the potential to cause weather extremes.

"La Niña is 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, which is 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 U.S.," Halpert continues. "Some of these factors, such as the North Atlantic Oscillation (NAO), 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 U.S."

Regional highlights include:

• Pacific Northwest: Weather is expected to be colder and wetter than average. La Niña often brings lower than average temperatures and increased mountain snow to the Pacific Northwest and western Montana during the winter months, which is good for replenishing water resources and winter recreation but can lead to greater flooding and avalanche concerns.
• California and the Southwest: Warmer and drier than average weather is expected. This likely will worsen 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: Weather likely will be colder and wetter than average and increased storminess and flooding is expected.
• Southern Plains, Gulf Coast States & Southeast: Weather is expected to be warmer and drier than average. This likely will worsen drought conditions in these areas and increase the risk of having above-normal wildfire conditions.
• Florida: Drier than average weather is expected, as well as an equal chance for above-, near- or below-normal temperatures and above-normal wildfire conditions.
• Ohio and Tennessee Valleys: Weather likely will be colder and wetter than average and increased storminess and flooding is expected.
• Northeast and Mid-Atlantic: There are equal chances for above-, near- or below-normal temperatures and precipitation. Winter weather for these regions often is driven not by La Niña but by weather patterns over the northern Atlantic Ocean and Arctic. These often are more short-term and generally are 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.: There are equal chances of above-, near- or below-normal temperatures and precipitation.
• Hawaii: Weather is expected to be drier than normal through November and wetter than normal December through February 2011. Statewide, the current drought is expected to continue through the winter, with several locations remaining on track to become the driest year on record. Drought recovery is more likely on the smaller islands of Kauai and Molokai and over the windward slopes of the Big Island and Maui.
• Alaska: Weather most likely will involve colder than average temperatures with equal chances of above- or below-normal precipitation. The interior and southern portions of the state currently are drier than normal. A dry winter may lead to a greater chance of above-normal wildfire conditions in the spring.

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

10/28/2010  

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