WASHINGTON -- Moisture-laden storms from the north, west and south are likely to converge on much of America over the next several days in what could be a once-in-a-generation onslaught, meteorologists forecast Tuesday.
If the gloomy computer models at the U.S. Climate Prediction Center are right, we'll see this terrible trio:
-- The "Pineapple Express," a series of warm wet storms heading east from Hawaii, drenching Southern California and the far Southwest, which already are beset with heavy rain and snow. It could cause flooding, avalanches and mudslides.
-- An "Arctic Express," a mass of cold air chugging south from Alaska and Canada, bringing frigid air and potentially heavy snow and ice to the usually mild-wintered Pacific Northwest.
-- An unnamed warm, moist storm system from the Gulf of Mexico drenching the already saturated Ohio, Tennessee and Mississippi valleys. Expect heavy river flooding and springlike tornadoes.
All three are likely to meet somewhere in the nation's midsection and cause even more problems, sparing only areas east of the Appalachian Mountains.
"You're talking a two- or three-times-a-century type of thing," said prediction center senior meteorologist James Wagner, who's been forecasting storms since 1965. "It's a pattern that has a little bit of everything."
While the predicted onslaught is nothing compared with the tsunami that ravaged South Asia last week, the combo storms could damage property and cause a few deaths.
The exact time and place of the predicted one-two-three punch changes slightly with every new forecast. But in its weekly "hazards assessment," the National Weather Service alerted meteorologists and disaster specialists Tuesday that flooding and frigid weather could start as early as Friday and stretch into early next week, if not longer.
"It's a situation that looks pretty potent," Ed O'Lenic, the Climate Prediction Center's operations chief, told Knight Ridder. "A large part of North America looks like it's going to be affected."
Kelly Redmond, the deputy director of the Western Regional Climate Center at the Desert Research Institute in Reno, Nev., where an unusual 18 inches of snow is on the ground already, said the expected heavy Western rains could cause avalanches. Since Oct. 1, Southern California and western Arizona have had three to four times the normal precipitation for the area.
"Somebody is in for something pretty darn interesting," Redmond said.
The last time a similar situation seemed to be brewing -- especially in the West -- was in January 1950, O'Lenic said. That month, 21 inches of snow hit Seattle, killing 13 people in an extended freeze, and Sunnyvale, Calif., got an unusual tornado.
The same scenario played out in 1937, when there was record flooding in the Ohio River Valley, said Wagner, of the prediction center.
Meteorologists caution that their predictions are only as good as their computer models. And forecasts get less accurate the farther into the future they attempt to predict.
"The models tend to overdo the formation of these really exciting weather formations for us," said Mike Wallace, a University of Washington atmospheric scientist.
Yet the more Wallace studied the models the more he became convinced that something wicked was coming this way.
"It all fits together nicely," Wallace said. "There's going to be weather in the headlines this weekend, that's for sure."
Wagner was worried about the Ohio and Tennessee River valleys as the places where the three nasty storm systems could meet, probably with snow, thunderstorms, severe ice storms and flooding. Some of those areas already are flooded.
The converging storms are being steered by high-pressure ridges off Alaska and Florida and are part of a temporary change in world climate conditions, O'Lenic said.
Over equatorial Indonesia, east of where the tsunami hit, meteorologists have identified a weather-making phenomenon called the Madden-Julian Oscillation. It's producing extra-stormy weather to its east. Similar oscillations in the north Atlantic and north Pacific are changing global weather patterns. Add to the strange mix this year's mild El Niño -- a warming of the equatorial Pacific -- which is unusually far west, Redmond said.
There's also another, more playful explanation: The nation's weathermen are about to converge on Southern California, and they bring bad weather with them.
The American Meteorological Society will meet next week in usually tranquil San Diego, which should be hit with the predicted storms and accompanying flooding in time for the group's gathering.
In 1987, when the meteorologists met in San Antonio for their convention, the city had ice storms. In 1993, when they gathered in Anaheim, Calif., it rained for 4.5 out of five days and triggered mudslides. Atlanta got rare snow during the meteorologists' 1996 convention. And in 2003 in Long Beach, Calif., heavy rain greeted them.
Ron McPherson, the group's recently retired executive director, said: "It always rains on the weatherman's parade."
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For more information on the Web, check out the Climate Prediction Center's weekly hazard assessment, at http://www.cpc.ncep.noaa.gov/products/predictions/threats/index_gloss.html