The California Highway Patrol escorted some drivers on the 5 Freeway in the Grapevine area until about 6:20 a.m. when snow tapered off and conditions improved.
Caltrans also warned drivers of hazardous conditions along the 15 Freeway through the Cajon Pass after heavy snowfall blanketed the area overnight.
Snow conditions have begun in the Cajon Pass on I-15. Avoid travel if possible. Use extreme caution while driving and keep moving to avoid getting your vehicle stuck in snow. Be safe out there! pic.twitter.com/iSRUX0CRMQ— Caltrans District 8 (@Caltrans8) March 10, 2021
A winter storm warning is in effect until 10 p.m. Thursday for the Los Angeles County mountains, excluding the Santa Monica range. The National Weather Service warned of possible snow accumulations of 2 to 5 inches in the mountains between 3,000 and 4,000 feet; 6 to 12 inches between 4,000 and 5,000 feet; and 12 to 20 inches above 5,000 feet. In addition, local amounts of between 24 and 28 inches are possible for favored locations, primarily above 6,000 feet.
The heaviest snow is expected on Wednesday, the NWS said.
"Significant travel impacts are possible for major mountain passes, including Cajon Pass and I-8,'' the weather service said. "Areas of dense fog will significantly reduce visibility at times, making travel more hazardous. Locally strong west winds with gusts 35 to 50 mph may impact some mountain areas. The combination of heavy snow and gusty winds may result in some downed tree limbs and power outages.''
WATCH: Winter storm dumps snow along Cajon Pass
For lower-elevation areas, rain is in the forecast through Friday, tapering off that night.
"Rain will become likely across all but southern and eastern L.A. County by late Tuesday night, where there will be a chance of rain, then rain is expected across the region Wednesday,'' according to the NWS.
Forecasters said the rain will be heavy at times on Wednesday.
"Rainfall totals are generally expected to average one-half to one inch, except locally 1.5 inches or possibly higher in the foothills and mountains below the snow level,'' according to the NWS.
Dry weather is expected to return by Friday night and continue through the weekend.
RELATED: Rain and snow return to SoCal, causing slick roads and bringing threat of flooding
City News Service contributed to this report.