Cold Storm Could Snarl Holiday Traffic

A cold, blustery northern Pacific storm is expected to dump heavy rain and snow on Southern California today and snarl pre-Thanksgiving holiday traffic on what historically has been the busiest travel day of the year.

As much as an inch of rain is forecast for the Los Angeles Basin today and tonight, with up to 3 inches in some of the surrounding foothill communities. Forecasters said more than a foot of snow could fall on some of the taller San Gabriel and San Bernardino mountains, with the snow level dipping as low as 3,500 feet on Thanksgiving morning.

A winter storm-watch warning of hazardous driving conditions was issued for the Tehachapi Mountains north of Los Angeles as the storm approached Tuesday night. Forecasters said thunderclaps and hailstones could rattle Los Angeles this afternoon. The Automobile Club of Southern California said more than 5 million people are expected to take to the road in the western United States during the four-day holiday weekend.

“The traffic probably will start building about noon Wednesday, with backups getting in and out of Los Angeles in all directions,” said Officer Evan Robinson, a spokesman for the California Highway Patrol. “The hardest hit will be the routes through the mountains, the major highways leading to popular places like Palm Springs and the roads to the airports.”

Cora Fossett, a spokeswoman for the city Department of Airports, said that because of the anticipated crunch, travelers are being advised to arrive at Los Angeles International Airport at least two hours before the scheduled departure of domestic flights, and at least three hours before international flights.

“We usually have 200,000 passengers a day taking off from LAX,” she said. “On Wednesday, we expect 300,000.”

Rain began falling in the Bay Area on Tuesday night as the intense low-pressure system started heading down the coast toward Southern California.

“What we’ve got is a classic winter storm, strengthening as it moves south,” said John Sherwin, a meteorologist with WeatherData Inc., which provides forecasts for The Times. “This one has nothing to do with El Nino.”

Sherwin said the first showers from the storm should spatter sidewalks in northwest Los Angeles about dawn. He said “pretty steady rain” is expected throughout the basin by midmorning. “Then, in the afternoon, it could get kind of interesting. . . . Between 3 p.m. and 8 p.m., there’s a pretty good chance of some fairly severe thunderstorms, with good-sized hail and winds of up to 55 mph.”

Sherwin said the rain should taper off by Thanksgiving morning, and sunshine should start peeking though the clouds during the afternoon.

Thursday night, however, will be one of the chilliest so far this year, with thermometer readings dropping into the upper 30s in some parts of the San Fernando and San Gabriel valleys.

A gradual warming trend should begin Friday morning, with mostly clear skies and high temperatures near 70 degrees by midday Sunday.

“The Sunday afternoon traffic will probably still be pretty bad,” Sherwin said. “But at least the weather will be good.”