Heavy rains set to soak L.A.

A significant rainstorm is expected to barrel into Southern California late today, dumping up to 3 inches of rain over two days and prompting the National Weather Service to issue flash-flood warnings.

The storm, arriving via a cold system just south of the Gulf of Alaska, should bring the heaviest rains early Friday, through the morning rush hour. By afternoon, the rains should begin to dwindle, but the weekend is expected to be chilly, with temperatures hovering around 50 degrees.

The rains, which could range from 1 to 3 inches from downtown L.A. to the mountains, are expected to bring a considerable snowpack--with about 6 inches of snow at elevations of about 6,000 feet.

That’s good news for ski operators and water managers bedeviled by drought. But the rains will once again threaten to unleash mudslides and debris flows on wildfire-razed slopes.

“It won’t take much after the fires to cause debris flows,” said Stuart Seto, a weather specialist for the National Weather Service in Oxnard. “With less than a half inch of rain, we’re looking at possible flash flooding and debris flows.”

The arrival of the storm, which is expected to hit Northern California first, will decrease the size of waves which have been thumping homes in coastal communities such as San Clemente.

By about 6:30 a.m. today, swells that have thrilled countless surfers with their lengths could peak, said Bill Patzert, a climatologist for the Jet Propulsion Laboratory in La Canada-Flintridge who also is a surfer.

“If I definitely wanted to put myself out and go out as a good-looking corpse, I’d go out this afternoon,” Patzert said Wednesday, as impressive waves crashed along the coast. “This surf is for young guys. No brain, no pain.”

But as the storm gets closer today, the wave lengths will become shorter and choppier, he said.

“Then you get storm surf -- what they call junk surf,” Patzert said. “Last year was a bad surf year. Surfers have been waiting for this for over a year.”

The storm could bring the last substantial rainfall the region gets for a while, said Eric Wilhelm, a meteorologist for www.accuweather.com. The overall winter forecast for Southern California calls for dry conditions.

Wilhelm said this storm should provide Las Vegas and Phoenix with quite a bit of rain Saturday and Sunday, then move toward Texas and finally on to the Eastern seaboard in a greatly diminished state.

Seto said there’s a chance of showers and thunderstorms Saturday. Unlike last week’s storm, Seto said, this storm will be stronger and will travel like a sheet through a much larger area, from Northern California to San Diego County.

Patzert said Los Angeles has not gotten more than an inch of rain in any single month since April 2006. That dry streak could end with this storm, he said.

He said the rain total for L.A. since July 1, when the rain year begins, is “100% of normal.” If this storm does what it’s forecasted to do, L.A. would have a perfectly normal December.

Given how dry it has been in the last 19 months, normal is welcome, Patzert said.

“Our winters are normally North Pacific storms preceded and followed by Santa Anas,” Patzert said. “So in some ways, this week is an example of who we are meteorologically. With a little bonus thrown in -- a little snow and a little surf thrown on top.”

hector.becerra@latimes.com