"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."