Warmer-than-average temperatures are expected this winter in an enormous area stretching from Arkansas west through Arizona and north as far as the Canadian border, as well as the northern two-thirds of Alaska, according to forecasters at the National Oceanic and Atmospheric Administration (NOAA).

Most of the rest of the United States can expect temperatures to average about normal from December through February, though cooler-than-average temperatures are expected in Hawaii and Florida (excluding the panhandle), the forecasters said.

An “indecisive” El Nino event, which had been expected to influence winter weather in North America, is complicating winter weather forecasting, according to Mike Halpert, deputy director of NOAA’s Climate Prediction Center.

“Typically, by mid-October we have a clear picture of the emerging climate factors that will influence the winter season, including whether El Nino or La Nina will occur. That has not been the case this year, however,” Halpert said. “A few months ago, El Nino appeared likely to develop and persist through the winter, but its development abruptly halted last month, and sea surface temperatures across the Pacific have largely returned to normal. We do still see some signs, however, that El Nino could still develop over the next few months, and that possibility was taken into account for this outlook.”

If El Nino — the warming of water temperatures in the central and equatorial Pacific Ocean — were to strengthen, NOAA’s temperature outlook for the winter months could change significantly, Halpert said.

“If we were to see El Nino intensify, the major shift to the temperature forecast would be the likelihood of more below-average temperatures across the South…maybe in coastal Texas and across the Gulf Coast. Potentially, the warm area would shift out of the Southwest as well,” Halpert said.

What caused the El Nino to recede is unclear, Halpert said. “It is unique in the roughly 60 years of data, but that’s still a fairly small sample size. Why it’s happened is something that we really don’t know at this point. Certainly, our models didn’t pick up on that, particularly our computer models, the dynamical models, really favored this to develop. It just seemed like when ocean temperatures became warm enough we never saw any interaction with the atmosphere, and absent that interaction…temperatures just returned back toward normal.”

Forecasters at Andover, MA-based Weather Services International have said they expect much of the eastern United States will experience generally mild temperatures through the end of the year (see Daily GPI, Sept. 25). Their forecast was based in part on the faltering El Nino event.

Households heating with natural gas will spend an average of 15% more this winter than last year due to a relatively colder heating season, slightly higher residential gas prices and an increase in demand, according to the Energy Information Administration (see Daily GPI, Oct. 11). Winter was unseasonably warm last year, resulting in little additional demand and weak prices.

January through September was the warmest first nine months of the year in U.S. history, according to NOAA, and 2012 is likely to go down as one of the warmest on record for the Lower 48.

“Above-normal temperatures, including episodes of record and near-record warmth have been consistent since last fall,” said Deke Arndt, chief of climate monitoring at NOAA’s Climate Prediction Center.

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