El Niño is expected to influence winter weather in the U.S.

El Niño in the central and eastern equatorial Pacific Ocean is expected to significantly influence winter weather in the U.S. from December through February 2010, according to the National Oceanic and Atmospheric Administration (NOAA).

"We expect El Niño to strengthen and persist through the winter months, providing clues as to what the weather will be like during the period," says Mike Halpert, deputy director of the Climate Prediction Center, which is a division of the National Weather Service. "Warmer ocean water in the equatorial Pacific Ocean shifts the patterns of tropical rainfall, which, in turn, change the strength and position of the jet stream and storms over the Pacific Ocean and U.S.

"Other climate factors also are likely to 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."

Some highlights of NOAA's winter outlook include:
  • Warmer-than-average temperatures are favored across much of the western and central U.S., especially in the north central states from Montana to Wisconsin. Still, periodic outbreaks of cold air are possible.
  • Below-average temperatures are expected across the Southeast and mid-Atlantic from southern and eastern Texas to southern Pennsylvania and south through Florida.
  • Above-average precipitation is expected in the southern border states, especially Texas and Florida. With recent rainfall and more expected, current drought conditions should improve in central and southern Texas. However, tornado records suggest there also will be an increased chance of organized tornado activity for the Gulf Coast region this winter.
  • Drier-than-average conditions are expected in the Pacific Northwest and the Ohio and Tennessee River Valleys.
  • In the Northeast, there are equal chances for above-, near- or below-normal temperatures and precipitation. Winter weather in this region often is driven by weather patterns over the northern Atlantic Ocean and Arctic, such as the NOA. These patterns often are more short-term and generally are predictable only about a week in advance.
  • In California, it is slightly more likely there will be wetter-than-average conditions over the entire state.
  • In Alaska, milder-than-average temperatures are expected—except along the western coast. There are equal chances for above-, near- or below-median precipitation for most areas.
  • Hawaii can expect below-average temperatures and precipitation for the entire state.
NOAA's seasonal outlook does not predict total seasonal snowfall accumulations or where and when snowstorms may hit. Snow forecasts depend on winter storms, which generally are not predictable more than several days in advance.

For more information, visit www.noaa.gov.

Date : 11/6/2009