Jan. 19, 2010 — -- Now it's California's turn. Two weeks after the eastern U.S. suffered through a major cold snap, the second of three major storms in a row is coming onshore from the northern Pacific today, bringing 1 to 3 inches of rain to the California coast -- and with it, the threat of flooding and mudslides in the million acres stripped of foliage by wildfires last year.
All told, by the end of the week, some parts of California may get up to 20 inches of rain. The Mammoth Mountain ski area is expecting up to 10 feet of snow.
There was a tornado warning for southern Los Angeles County this afternoon -- a rarity in California.
Fifteen-foot waves crashed on Hermosa Beach, forcing officials to close the local pier. Piers in Ventura and Manhattan Beach were also being closed as a precaution, the Los Angeles Times reported.
During the first wave of storms Monday, rain and hail swept the San Francisco-Oakland area. Wind gusts of 59 mph were reported at San Francisco International Airport, forcing an American Airlines jet with minor mechanical problems to divert to San Jose where a landing would be easier.
It feels very different from the cold snap that the eastern two-thirds of the country suffered earlier this month -- but climate scientists say it is part of the same pattern, now shifted to the west.
"Thunderstorms will bring hazardous wind gusts and lightning to the area," the weather service warned in a statement for the Los Angeles basin. "High intensity rainfall could cause rock slides and debris flows as well as roadway flooding."
Some of the greatest risk was in the rugged terrain around La Canada Flintridge, Calif., just north of Los Angeles. Since the wildfires late last summer, there has been little foliage to anchor the soil, so when the rain comes, so does danger.
About 100 residents were told to evacuate Monday, and they were likely to have to leave again as the week goes on.
"We are begging you to leave when you're ordered," said Deputy Chief Mike Metro of the Los Angeles County fire department at a news conference. "We can't stop these debris flows."
"We got mud flowing into our backyard right now," said Steve Brown, a La Canada resident. Monday, in heavy rain, he and his family decided not to wait for the police to tell them to pull out.
"We're leaving. We can't do anything, so it's better to be safe and hope for the best," he said.
The western weather is part of larger phenomenon called the Arctic Oscillation, said William Patzert, a climate scientist at NASA's Jet Propulsion Laboratory in Pasadena, Calif. -- right near La Canada Flintridge. Shifts in the Arctic Oscillation can affect much of the northern hemisphere.
"While the rest of the country has been battered by strong, cold outbreaks bringing storms over the past two weeks, snow and frigid temperatures, California remained mild and dry," said Patzert in an e-mail to ABCNews.com. "Now it's our turn."
Western Storms: One-Two-Three Punch
Patzert said the Arctic Oscillation -- in which high pressure over temperate latitudes keeps the harshest Canadian storms from reaching us -- is now in a weak "negative phase," with higher pressure in polar regions pushing storms to the south.
"The jet stream is very powerful (more than 200 mph) and pushing these wet northern Pacific storms down the West Coast. This is the pattern that the rest of the U.S. has had in the past two weeks, but shifted farther west," said Patzert by e-mail.
"I call it the Yukon Express. There'll be cold storms the rest of the week."
The repeated storms are enough to bring heavy snow to parts of the Rockies, and rain to the Arizona desert.
In part, like the eastern cold two weeks ago, this is a routine part of winter; Los Angeles gets two-thirds of its annual rainfall between January and March. And there are silver linings in gray clouds: the storms will ease the western drought and bring much-needed snow to ski resorts.
Weather does change, by the way. Eastern cities that froze last week are much more mild now. It reached 49 degrees in New York and 64 in Atlanta this afternoon.
But this week's mudslide threat in California is an aberration.
"They're incredibly deadly," said Lucile Jones of the U.S. Geological Survey. "The only solution is to get out of the way before they come."