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...

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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 yesterday.

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, already beset with heavy rain and snow. Flooding, avalanches and mudslides are possible.

• 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.

Meteorologists caution that their predictions are only as good as their computer models. And forecasts are less accurate the further 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,” he said. “There’s going to be weather in the headlines this weekend, that’s for sure.”

The National Weather Service yesterday issued a statement warning that several inches of snow could fall by the end of the weekend in the central Puget Sound lowlands, including Seattle. The snow could begin as soon as tomorrow night, particularly in areas north of Seattle, with a growing chance of snow farther south Friday, the weather service said. Highs through this weekend are expected to be in the low- to mid-30s, with lows in the mid- to high-20s.

“Don’t sound the alarm,” weather service meteorologist Johnny Burg said. “But tell everybody to just pay attention to future forecasts.”

The three storms are likely to meet in the nation’s midsection and cause even more problems, sparing only areas east of the Appalachian Mountains. Property damage and a few deaths are likely, forecasters said.

“You’re talking a two- or three-times-a-century type of thing,” said prediction-center senior meteorologist James Wagner, who has been forecasting storms since 1965. “It’s a pattern that has a little bit of everything.”

The exact time and place of the predicted 1-2-3 punch changes slightly with every new forecast. But the National Weather Service, in its weekly “hazards assessment,” alerted meteorologists and disaster specialists yesterday 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,” said Ed O’Lenic, the Climate Prediction Center’s operations chief. “A large part of North America looks like it’s going to be affected.”

Kelly Redmond, 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, said the expected heavy Western rains could cause avalanches. Southern California and western Arizona have had three to four times the normal precipitation for the area since Oct. 1.

“Somebody is in for something pretty darn interesting,” Redmond said.

Somebody already knows.

A wintry blast yesterday closed schools and glazed roads with ice and snow in the Rockies and on the central Plains, a 40-mile stretch of Interstate 5 was closed north of Los Angeles after up to 3 feet of snow fell in the region, and new flooding hit northeast of Phoenix, killing one man and leaving another missing.

Various levels of winter-weather advisories and storm warnings were in effect into this morning from Arizona to Connecticut, the weather service said.

Up to 2 feet of snow was possible in Colorado, where one traffic fatality was blamed on the weather and an avalanche blocked U.S. 550 about 40 miles north of Durango, the weather service said.

The last time a similar situation seemed to be brewing — especially in the West — was in January 1950, O’Lenic said. Seattle received 21 inches of snow, killing 13 people in an extended freeze, and Sunnyvale, Calif., was the scene of 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.

He 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 a tsunami hit Dec. 26, 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 this year’s mild El Niño — a warming of the equatorial Pacific — which is unusually far west, Redmond said.

Seattle Times staff reporter Warren King contributed to this report; yesterday’s weather was reported by The Associated Press.