Accuweather’s official forecast for the 2012-2013 winter season is predicting big snowstorms for the Northeast and mid-Atlantic regions of the U.S. and wet weather for the Gulf Coast.
“As far as above-normal snowfall goes, from New York City on south and west has a better shot with more mixed rain and snow systems in New England," AccuWeather Lead Long-Range Forecaster Paul Pastelok said.
The Midwest, however, is likely to have less snow than usual in the coming months, which will keep temperatures down slightly this winter, AccuWeather predicts.
Things are looking particularly dry in the Northwest.
"I have big concerns about the Northwest as far as drought goes," Pastelok told AccuWeather. "We have already set up the stage here at the start of fall with wildfires and drought conditions. With the exception of a break with some rain and snow during October and early November, it will be drier than normal through the winter season and maybe even longer as we head toward spring."
Earlier this year, meteorologists were predicting the start of an El Niño event after several years in the grip of La Niña, but recent cooling in the Pacific Ocean has now undermined that possibility.
“Given the recent faltering of El Niño, I expect that near-average wind-shear levels will continue over the tropical Atlantic into November and that we will see one or two more tropical storms in the Atlantic this hurricane season,” Weather Underground writer Jeff Masters wrote Friday.
El Niño’s more proper name is the El Niño-Southern Oscillation, which actually covers both La Niña and El Niño events. The ENSO reflects whether the temperatures on the surface of the sea in the Equatorial Pacific Ocean are above or below a long-term average. If the sea surface temperatures are colder, it’s a La Niña season; higher, it’s El Niño.
ENSO is just one of three major factors that go into seasonal forecasts, as Accuweather writer Grace Muller points out in a Friday blog post. Meteorologists also look at the North Atlantic Oscillation, which compares temperatures off the coast of Spain to the northernmost reaches of the Atlantic Ocean. Negative NAO, which occurs when it is colder than usual in Spain and warmer than usual far north, tends to block weather systems from moving out to the ocean and forces cold air masses down into the Eastern U.S.
Weather forecasts also factor in "analog years" by examining years that had similar precipitation and temperature patterns in the previous season.