October 16, 2009

NOAA: Colder Winter In South, Warmer In North, West

The Southeastern United States will have a colder, wetter winter season this year, while warmer conditions will prevail in the Midwest and Northern U.S., according to the 2009 Winter Outlook released Thursday by the National Oceanic and Atmospheric Administration (NOAA).

"El Niño in the central and eastern equatorial Pacific Ocean is expected to be a dominant climate factor that will influence the December through February winter weather in the United States," said the agency.

An El Niño weather event is when parts of the Pacific Ocean heat up, affecting weather patterns throughout the world.  Forecasters predict this year's El Niño, which is currently weak but is expected to strengthen in the next few weeks, to play a major role in America's winter temperatures.

"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," said Mike Halpert, deputy director of the Climate Prediction Center "“ a division of the National Weather Service.

"Warmer ocean water in the equatorial Pacific shifts the patterns of tropical rainfall that in turn change the strength and position of the jetstream and storms over the Pacific Ocean and the U.S."

"Other climate factors are also likely to play a role in the winter weather at times across the country," said Halpert, adding that 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 country," he said.

Forecasters are predicting warmer-than-average temperatures across much of the western and central U.S., particularly in the north-central states from Montana to Wisconsin. But occasional outbreaks of cold air are still possible.

Alaska also has a higher probability of warmer temperatures, except along its western coast.

Below-average temperatures are forecast for the Southeast and mid-Atlantic states, from southern and eastern Texas to southern Pennsylvania and south through Florida, NOAA said.  

Below-average temperatures and precipitation are also predicted across the entire state of Hawaii.

Some areas of the country, such as the Northeast and California, have equal chances for above-, near-, or below-normal temperatures and precipitation, according to the forecast.
NOAA said it is expecting above-average precipitation throughout the southern border states, particularly in Florida and Texas, with an increased chance of tornado activity for the Gulf Coast region.

Meanwhile, drier-than-average conditions are expected in the Pacific Northwest and the Ohio and Tennessee River Valleys.

Overall, a little more than half of the U.S. by area will have warmer-than-normal temperatures.  The rest can expect cooler conditions, Halpert said.

The El Niño will help some regions currently experiencing drought conditions, with significantly higher probabilities of wetter winters forecast for California, Texas and Florida along with parts of southern New Mexico, Arizona, Louisiana, Mississippi, Alabama, Georgia and South Carolina, Halpert said.

Hawaii, the Pacific Northwest and a swath of the Midwest from Michigan to Arkansas will likely be drier than normal due to fewer storms, he said.

Such weather may not be good news for next year's winter Olympics in Vancouver, British Columbia, where Halpert predicts a "dry and warm winter".

However, "it certainly can be cool enough for snow," he said.

The El Niño not only influences the forecast, but it gives scientists more confidence that what they predict will come true, Halpert said.

Temperatures in September were warmer than normal in the U.S., but not by a great extent, while national rainfall levels were exactly average.  The month ranked 32nd out of 115 Septembers on record.  

However, Nevada saw its warmest September on record, while California tied for its warmest month on record.

The forecast can be viewed at NOAA's Web site at