LOS ANGELES >> A cold and blustery winter storm unleashed downpours and extensive snowfall on Southern California, triggering tornado warnings and snarling post-Christmas travel on major routes today.

Snow shut down vital Interstate 5 in Tejon Pass through the mountains north of Los Angeles and stopped traffic on Interstate 15 over Cajon Pass in the inland region to the east. The southbound side of I-15 finally reopened, but the northbound side remained closed well into the day.

A truck driver was found unresponsive in a rig stopped along I-5 in Tejon Pass. Kern County firefighters pronounced him dead, according to the California Highway Patrol’s online incident log.

It was not immediately known if the death was weather-related. Phone and email messages seeking comment were not immediately returned from the Kern County Sheriff’s Office, where the sheriff also serves as county coroner.

After being stuck for five hours in Cajon Pass, motorist Johnny Lim wasn’t sure he could reach Las Vegas, where he hoped to spend time after Christmas. He worried about driving his car through the pass when it reopens.

“The freeway is full of snow and ice,” he said, adding that his car “is not built for conditions like this.”

I-5 rises to more than 4,100 feet in Tejon Pass between Los Angeles and the San Joaquin Valley. Cajon Pass rises to more than 3,700 feet between the San Gabriel and San Bernardino Mountains on I-15, the major connector between Southern California and Las Vegas.

Southbound I-15 also was closed by snow in the community of Primm, Nevada.

Snow also stopped or slowed traffic on other California roads, including heavily traveled Interstate 8 in eastern San Diego County, and numerous trees were toppled.

The storm began unleashing waves of pounding rain in the region on Christmas Day and continued into today.

Localized flooding inundated roads and freeway lanes while snow fell to low elevations, leading to numerous traffic accidents.

The town of Wrightwood at the eastern end of the San Gabriel Mountains had received 25 inches of snow by midday.

Famed Palomar Observatory in the San Diego County mountains said it would be closed at least through the weekend because of heavy snowfall.

The tempest triggered tornado warnings overnight in Santa Barbara and Orange counties when radar indicated rotation in severe thunderstorms. The warnings were later canceled.

The National Weather Service said the heaviest rain moved east of Los Angeles County before dawn but that showers were expected to continue through the day.