1st Rains of a Wet Winter Expected : Weather: Forecasts prompt some residents to sandbag against mudslides on fire-ravaged hillsides. A recurrence of last year’s El Nino-spawned drenching is predicted.

Rain began falling Wednesday night in Los Angeles County, and forecasters say it may be the start of another very wet winter.

And these prospects for rain--a little now, a lot more in the months to come--are raising concerns about destructive mudslides on the fire-ravaged hillsides of Southern California.

The modest amounts of rain expected through today would come from a small arctic storm that has been working its way south along the coast of California--typical weather for this time of year.

Unusually strong storms expected later would be the product of El Nino, a little-understood weather phenomenon that for the first time in half a century appears to be returning for the second consecutive year.

Last winter’s drenching storms destroyed homes, buried highways and killed more than a dozen people in Southern California and northern Mexico. Officials say that similar rains this winter--falling on burned slopes stripped of the vegetation needed to hold the soil in place--could cause even more damage.

“If we get those rains again, things could be really bad,” said Angel Montoya, an inspector with the Los Angeles County Fire Department. “Sandbags are already being made available in all the fire areas. People should start getting ready now.”

On Wednesday, sand scooped up from Zuma Beach was hauled to a fire station at Monte Nido--the heart of last week’s Calabasas/Malibu fire area. There, residents concerned about today’s runoff filled green nylon bags with the sand before hurrying home to build barriers.

County Fire Capt. Paul Donohue said concerned residents waited patiently in line for bags at the Malibu fire station early Wednesday morning. “And business always picks up after the first rain,” Donohue said.

There is a good chance of rain throughout the Los Angeles Basin into today, with about a quarter of an inch along the coast and perhaps twice that much in the foothills, forecasters said. They said the snow level should be about 6,000 to 7,000 feet, with an inch or two accumulating at ski resort levels.

Temperatures should be pleasant, with highs in the upper 60s and lower 70s in the coastal valleys after overnight lows in the mid-40s to mid-50s.

Skies are expected to start clearing by this afternoon, with breezy, generally sunny conditions Friday.

Although rainfall from this system won’t be dramatic, James McCutcheon, a meteorologist with WeatherData Inc., said conditions are already shaping up for a return of the brutal storms that hammered Southern California last year. And once again, he said, El Nino--named for the Christ child because the storms it spawns were first observed at Christmastime--is to blame.

The phenomenon, which prevailed in the winter of 1992-1993 after about an eight-year hiatus, is thought to have caused last winter’s unusually wet conditions in California and extreme cold in the eastern United States, as well as contributing to severe spring and summer flooding in the Midwest.

Meteorologists say that El Nino conditions begin when the equatorial trade winds in the southern Pacific, which normally flow from east to west, reverse direction. Pushed by the shifting winds, large bodies of warm water that normally circulate near Australia drift slowly east in what is called a Kelvin wave, pooling off the west coast of Peru.

For years, the only way this wave was detected was by the abnormally small fish catches off Peru, where an El Nino deprives the waters of nutrients normally brought to the surface by cooler currents from below.

Today, the Kelvin wave shows up on radar sensors aboard a space satellite monitored by NASA. Because the warm water of the Kelvin wave is less dense than the cooler water surrounding it, it forms a bulge about six inches high on the surface of the Pacific, an altitude differential that the radar can detect.

Recent observations from the satellite have confirmed what the National Oceanographic and Atmospheric Administration suspected: The bulge is back.

McCutcheon said that means that the subtropical jet stream--which moves from west to east across the Pacific near Hawaii--will begin to strengthen. Masses of warm, moist air off the east coast of Hawaii will begin drifting toward Southern California, bringing with them increasing chances of substantial rain.

“From now on, you’ll be having to keep your eyes open,” McCutcheon said. “There’s a band of moisture off Hawaii right now. That one probably won’t get here. But that type of pattern is starting to evolve. And the chances of the rain getting here improve as time goes along.”

McCutcheon said really heavy downpours usually occur when the warm, moist air from Hawaii collides over Southern California with the sort of cold front from the Gulf of Alaska that is bringing the rain expected today.

“If you had to make your wager right now, I’d bet on another wet winter in Southern California,” McCutcheon said.

Times staff writer Chip Johnson contributed to this story.