This post has been updated below.
Snow was falling in Southern California mountain areas Thursday night as cold air was expected to drop snow levels to 3,500 feet.
The National Weather Service said that six to 12 inches of snow was expected to fall in the San Gabriel Mountains. In the Antelope Valley foothills, three to six inches of snow could fall.
On Thursday night, fire and police crews were searching for at least person who may have been trapped on an island in the Santa Ana riverbed in Colton in San Bernardino County, police said. A law enforcement helicopter was flying above the rain-swollen river as crews tried to determine whether anyone was stranded.
[Updated 10:11 p.m.: A man was hoisted out of the area by the helicopter crew, according to television news footage.]
Across Southern California, snow levels were expected to drop to 3,500 feet to 4,000 feet.
"The cold air drops snow levels like a rock on the north slopes of the mountains and the Antelope Valley foothills," the weather service said in a statement.
Rain and snow were also reported in the San Bernardino Mountains, where more than two inches of rain fell at Lake Arrowhead, according to the weather service.
Winter storm warnings were posted across Los Angeles and San Bernardino counties. Wind gusts around 30 mph were predicted from some areas.
Officials announced that roads in the Angeles National Forest would be closed through early Friday because of the snow.
The closures affected Angeles Forest Highway between Aliso Canyon Road and Upper Big Tujunga Canyon Road, the Sheriff's Department said.
Upper Big Tujunga Road was also closed between Angeles Crest Highway and Angeles Forest Highway.
Earlier Thursday, rain flooded roads and sent mud and debris flowing across highways in mountain areas, officials said.
From 1 a.m. to 6 p.m., there were about 240 collisions reported on Los Angeles-area roadways, compared to 134 in the same period a week earlier, according to the California Highway Patrol.
Officials in Redlands said mud and debris forced the closure of San Timoteo Canyon Road from Live Oak Canyon Road to Barton Road. The area was expected to be shut down throughout the night.
As of Thursday evening, 0.34 of an inch of rain had fallen in downtown Los Angeles and 0.72 of an inch was recorded in Pasadena, the weather service said.
In Orange County, Lake Forest recorded 0.72 of an inch of rain and San Bernardino in the Inland Empire recorded an inch of rain.
The cold, wet weather was expected to last through Friday night.