WASHINGTON — Winter 2011-12 is likely to be an encore of last winter for much of the northern United States, with the worst cold and snow concentrated around the Great Lakes, and drought continuing and expanding from the Southwest states to Florida, government and private forecasters predict.
The formal National Weather Service outlook for December through February, issued Thursday, anticipates that a weak episode of cool water temperatures in the Pacific will steer cold and wet conditions across the northern tier, while leaving Arizona to Florida warmer and drier than normal.
Ninety-one percent of Texas and 87 percent of Oklahoma are already under the weather service’s top two drought categories, with Texas experiencing its driest 12-month period on record through the end of September.
“The summer tropical storm season didn’t provide the drought relief we’d hoped for in theses areas, and it will take 10 to 15 inches of rain over the next few months to make much difference,” said David Brown, director of regional climate services for the NWS Southern Regional office in Fort Worth.
“Unfortunately, with the La Nina over the winter, the likelihood of seeing that is pretty low,” although he noted that not every La Nina event robs the region of moisture. “We could still see a curveball.”
Those same historical patterns suggest that Florida, despite some recent soakings, is likely to see drought conditions develop, particularly across the southern half of the peninsula, by winter’s end. Drier-than-normal conditions are expected from the central Gulf Coast up the southern seaboard to Virginia.
The outlook says it’s likely that conditions will be wetter than average from the Pacific Northwest into the Rockies and across the northern Plains to the Great Lakes and Ohio and Tennessee valleys, with cooler-than-normal conditions along most of the Pacific Coast and the top of the country as far east as western New York.
Similar patterns have been predicted by the private forecasting service, Accuweather.com, which unlike the Weather Service, also makes early snowfall estimates. It warns of more blizzards for Chicago and Minneapolis, although with snow piles somewhat smaller than last winter’s.
As far as the Northeast and mid-Atlantic states go, temperatures and precipitation are likely to be less extreme than last winter in New York, Philadelphia and Baltimore, with New England a bit more likely to have normal snowfall or better.
Mike Halpert, deputy director of the Climate Prediction Center at the National Oceanic and Atmospheric Administration, said while La Nina is the major factor now, “there is a wild card in the form of another phenomenon called the Arctic Oscillation that can generate strong shifts in climate patterns” and could trump La Nina.
The Arctic Oscillation has two phases — in its positive state, it keeps cold air locked up over northern Canada; in its negative state, it allows that cold air to spill south and bring winter weather much deeper into the U.S. Those slips were responsible for most of the storms that hit the South and East Coast the past two winters, and could occur again, Halpert noted.
However, forecasters say the Arctic patterns usually last just a few weeks and generally can’t be forecast more than a week or two ahead of time.
To see the winter outlook, got to http://www.cpc.ncep.noaa.gov/products/predictions/long_range/fxus05.html.