Powerful Storm Hits Southland : Weather: Gulf of Alaska system dumps heavy rain and snow, prompting mudslide alerts and tormenting commuters. More is likely, forecasters say.

A potent storm from the Gulf of Alaska dumped substantial rain and snow on Southern California on Tuesday, snarling traffic with accidents and flooded intersections, blocking mountain passes with wind-whipped snowdrifts and prompting mudslide warnings below fire-scarred hillsides.

More than 1 1/2 inches of rain fell in some foothill communities by nightfall, with nearly a foot of new snow reported at some mountain resorts. Forecasters said those totals could double before the complex weather system finally moves out of the Southland sometime Thursday afternoon. The first major storm of the winter struck Southern California about 2 a.m. Tuesday, and by dawn the steady rainfall in the coastal valleys was accompanied by a heavy frosting of snow in the San Gabriel and San Bernardino mountains.

Interstate 5--California’s principal north-south highway--was closed by heavy snow and gusting winds near the Tejon Pass at about 8 a.m. Officials said it took Caltrans crews more than three hours to reopen the roadway. There were concerns that more snow during the night could again block the pass through the Tehachapis 75 miles north of Los Angeles, before dawn today.

About three inches of snow fell in Palmdale and in other high-lying areas of the Antelope Valley. Roads there remained open, but the commuter drive slowed to a crawl.

Little snow fell on Interstate 15--which traverses the San Bernardino Mountains through Cajon Pass, 20 miles north of San Bernardino--but southbound lanes in the pass were closed temporarily by a crash involving two big-rig trucks and three other vehicles. The California Highway Patrol said that because of high winds and fog in the pass, high-profile vehicles were advised to use alternate routes.

In the Los Angeles metropolitan area, the problem was rain, not snow.

Morning commuters faced a triple threat: A wave of back-to-work traffic after an extended holiday weekend; flooded intersections in low-lying areas that stalled a number of cars and a rash of traffic accidents on the rain-slick pavement.

The CHP said it logged more than 250 accident calls on Los Angeles County freeways between 8 a.m. and noon--nearly four times the usual number during dry weather.

The accidents, for the most part, were minor, with few serious injuries reported. But some of the mishaps disabled large trucks, and the sprawled wreckage contributed to the traffic tie-ups.

A pressurized tanker truck carrying liquid oxygen crashed in the westbound lanes of the Foothill Freeway in downtown Pasadena at 6 a.m. Tuesday. The tank ruptured, and the spewing gas forced closure of several traffic lanes.

Several hours later, a big rig jackknifed into the center divider of the same freeway in Irwindale, blocking traffic until the debris could be cleared. Another big truck jackknifed across several lanes of traffic on the Golden State Freeway in the Sylmar area, creating a tie-up there.

The National Weather Service issued a flash-flood warning of possible mudslides in the Topanga Canyon, Malibu, Altadena and Laguna Beach communities--areas stripped of soil-holding vegetation during disastrous brush fires in the fall of 1993.

By nightfall Tuesday, no slides had been reported, but forecasters said additional rain was expected before dawn. Occasional moderate showers were forecast for today, with more heavy rain tonight.

Curtis Brack, a meteorologist with WeatherData Inc., said the storm system, born in the frigid environs of the Gulf of Alaska, moved south along the West Coast before heading inland with a three-pronged attack.

First, one of the storm’s three moisture-laden arms moved in across Southern California before dawn Tuesday, accounting for much of Tuesday’s rain and snow. The second segment began moving inland after nightfall and the third was due about noon today.

Brack said skies are expected to clear Thursday afternoon, with mostly fair weather through the weekend.

The Weather Service said 0.45 of an inch of rain had fallen at the Los Angeles Civic Center by 5 p.m. Tuesday, raising the season’s total there to 2.6 inches. The normal Jan. 3 total for the season, which runs from July 1 through June 30, is 5.16 inches.

Other daily totals as of 5 p.m. Tuesday included 1.97 inches at the Santa Barbara Airport, 1.53 in Avalon, 1.34 in Torrance, 1.22 in Rendondo Beach, 1.04 in Newhall, 0.91 of an inch in Woodland Hills, 0.53 in Monrovia, 0.38 in Anaheim and 0.10 in El Toro.

Tuesday’s high temperature in Downtown Los Angeles was 59 degrees, after an overnight low of 52. Similar temperatures are expected today and Thursday.

The continuing storm led Los Angeles County health officials to issue a pollution warning recommending that beach visitors stay out of the water until at least 72 hours after the rain has stopped.

Beach-goers were reminded that billions of gallons of runoff--much of it contaminated with animal droppings, trash, oil, grease, pesticides, fertilizers, chemical residue and other pollutants--flow through area storm drains into coastal waters every time there is substantial rain. In the case of unusually severe pollution, beaches are closed.

Times staff writers Henry Chu and Jeanette DeSantis in the San Fernando Valley and Tom Gorman in San Bernardino contributed to this story.