An Unexpected Storm Drops In : Weather: Rain snarls Southland commuter traffic. Heavy snow in the mountains closes two highways.

A cold, blustery winter storm descended unexpectedly on Southern California on Tuesday, snarling commuter traffic with rain showers and dropping heavy snow in the mountains that closed Interstate 5 near Gorman and the Antelope Valley Freeway near Agua Dulce.

By 5 p.m., 0.25 of an inch of rain had fallen on the Los Angeles Civic Center, raising the season’s total to 5.53 inches, 0.40 of an inch above the normal seasonal total for the date.

The high temperature in downtown Los Angeles was only 51 degrees. That was just four degrees above the normal low temperature for the date and just one degree above the coldest maximum ever recorded here on Jan. 7, 1913--a 50-degree reading.

The rain slowed commuters during both the morning and evening rush hours, triggering dozens of minor fender-benders, according to the California Highway Patrol.

The snow, which dusted the Tehachapi, San Gabriel and San Bernardino mountains throughout the day, began falling heavily in the late afternoon.

At 4:10 p.m., the CHP was forced to close I-5 in both directions on the Grapevine grade, sending traffic on a 100-mile detour through the Antelope Valley. The detour itself was blocked half an hour later when snow clogged the Antelope Valley Freeway near Agua Dulce.

Chains were required above 1,500 feet throughout the San Bernardino Mountains.

San Bernardino County sheriff’s search and rescue teams using skis, snow-cats and snowmobiles searched the high-mountain backcountry between Lake Arrowhead and Big Bear Lake on Tuesday for a couple feared stranded in up to six feet of snow.

Deputy Mark Youngblood, coordinator of the search effort, said Stephen Stevens, 24, of Fullerton and Cheryl McCaslin, 23, of Anaheim had used a four-wheel-drive vehicle to traverse a rough U.S. Forest Service road between the two lakes about 10 days ago. It was feared they may have attempted the trip again during last weekend’s heavy storm.

Youngblood said the couple were last seen about 7 a.m. Sunday. The search was begun after they failed to show up for work on Monday.

The storm, which originated in the Gulf of Alaska, had been expected to move eastward across Northern California, leaving Central and Southern California largely unscathed.

Instead, the wet, windy weather system rode high-altitude jet-stream winds south along the coast, slamming into the seaside community of Half Moon Bay, about 80 miles south of San Francisco, a few hours before dawn.

Gusts of more than 40 m.p.h. intensified as they swept through a coastal canyon, damaging at least 30 mobile homes at the Canada Cove Mobile Home Park.

“It took some of the carports and threw them 20 feet away,” said Ed Dudley, manager of the park. “Some of the supports for awnings drove right through the sides of the houses. . . . It was like a tornado went through.”

Rain began falling in the Los Angeles area at about 8 a.m., and showers continued, off and on, throughout the day, intensifying in some areas at nightfall.

Totals from the storm by 5 p.m. Tuesday included Culver City, 0.55 of an inch; Santa Monica, 0.53; Monrovia, 0.49; Pasadena, 0.45, Glendale, 0.43, San Juan Caspistrano, 0.30, and San Bernardino, 0.26.

Heavy surf pounded seaside homes in the Rincon area, between Ventura and Santa Barbara, but no major damage was reported.

Steve Burback, a meteorologist with WeatherData Inc., said the storm should have moved out to the east by dawn today, leaving clear skies and high temperatures from the mid-50s to the mid-60s.

He said a large clear-weather system should start filling in behind the storm this afternoon, generating winds of up to 35 m.p.h. below canyons tonight and Thursday morning. High temperatures Thursday should range from the mid-60s to the mid-70s.

Another, weaker storm system is expected to bypass Southern California on Friday, with generally clear weather on Saturday, but Burback said a third storm, moving this way, could bring additional rain by Sunday.