The National Weather Service yesterday warned of a likely "stormy, wet winter" for the Washington area, presaging a possible repeat of last year's winter that included freak back-to-back storms that dumped more than 20 inches of snow here.
Donald L. Gilman, chief long-range forecaster for the weather service, said current air pressure and wind patterns over the Pacific Ocean and West Coast have created a 60 percent chance that the Atlantic coast, including Washington, will experience greater-than-normal precipitation -- meaning more rain and possibly more snow than usual.
How much more snow? That depends on how cold it gets, Gilman told reporters at his annual winter forecast news conference.
He said his meteorological tea leaves have not given him specific enough signals this year to say whether temperatures will run above or below average.
Gilman said Washington is subject to wildly varying conditions, as in the record-breaking 12-inch snowstorm that unexpectedly hit the city Nov. 11. Thus, the chance of another cold snap coinciding with a sudden dose of precipitation later this winter should not be dismissed lightly, Gilman said.
Couching his remarks in such phrases as, "if we are right," and "assuming we are correct," Gilman said long-range forecasting is based "only on statistical hints and clues . . . which we label with probabilities."
For the rest of the nation, Gilman said the greatest likelihood of colder-than-normal weather is in the Midwest and Deep South, with the Southwest likely to have unseasonably mild conditions.
The chances of below-normal temperatures exceed 55 percent from Wisconsin and eastern Iowa, Missouri, Arkansas and Texas to the Appalachian mountains and northern Florida, he said.
They reach 60 percent in much of Michigan, Indiana and Ohio, as well as eastern Louisiana and parts of Alabama and the Florida panhandle, he said.
Temperatures have a 55 percent chance of being above normal from the New Mexico and Colorado Rockies west to California and parts of central Oregon and Washingon, according to Gilman, with a 60 to 65 percent chance in the canyon country of Utah and Arizona, as well as coastal Oregon and Washington.
Precipitation, he said, has a 55 percent chance of falling short of normal from California east to the southern Rockies, the Great Plains and the lower Missouri valley.
There are "equal chances" of below- or above-normal precipitation for the northern tier of states from the West Coast to the Great Lakes and from the Louisiana Gulf region north to Ohio and Indiana, Gilman said.
For the East Coast, Gilman said a "stormy wet zone," similar to the one last winter, should extend from Mississippi east to central Florida and then curve north along the Atlantic to New England.
He said there is some evidence that last winter's storms here were triggered by an intensification of El Nino, the current of warm water in the Pacific Ocean west of South America. But he said it is uncertain whether its influence will continue this winter.
"It is rare for it to last two winters in a row," he said, "but it can happen."
The current, which brings unusual, near-90-degree water east from the Solomon Islands, is believed to influence weather patterns over much of the United States, along with other weather activity to the west of North America.
Regardless of El Nino's mood, Gilman said, the wetter-than-usual weather expected here this winter will come from other sources -- patterns of high pressure over the northwestern United States and countervailing low pressure areas over the northern Pacific and central Canada.
Asked whether Washington should expect a white Christmas, Gilman said, "That's too chancy. It just depends on what happens from day to day."