The rain, largely scattered showers, was expected to be light -- less than a 10th of an inch in coastal and valley areas, according to the National Weather Service.
But the snow level rapidly fell to between 2,000 and 3,000 feet, and authorities shut down Interstate 5 in the area of The Grapevine because of snow for a time this morning. When the road was open, vehicles were being escorted by the California Highway Patrol.
Brief snow showers are also possible across the Antelope Valley (14) Freeway and Pearblossom (138) Highway, but under an inch of accumulation is likely, according to NWS forecasters.
Snow showers were expected to continue through Friday morning, but accumulation was expected to add up only to one or two inches. Nonetheless, roads will be challenging.
"People traveling into the mountains during the next few days are urged to prepare for extremely cold temperatures and dangerously low wind chills," according to an NWS advisory. "Roads could be icy and treacherous. Areas of black ice are possible ..."
The quick-moving storm's salient element was expected to be the wind, with gusts of around 60 miles per hour reported in the Los Angeles county portion of the San Gabriel mountains this morning. Gusts of around 40 mph were recorded in Malibu and the Antelope Valley.
At the same time, temperatures were dropping precipitously, with highs expected to be in the 40s and 50s along the coast and in the valleys and the 20s and 30s in the mountains, NWS forecasters said.
Saturday morning is expected to be particularly cold, with temperatures dropping into the 20s in valley areas, "resulting in a potentially damaging freeze event," according to an NWS advisory.
"Farmers and anyone with sensitive plants or animals should prepare for several nights of very old and potentially sub-freezing temperatures," it said, adding that Friday night and Saturday night will be the coldest of the cold spell, and plants and crops will be threatened.
A high wind warning indicating 40-hour winds or gusts of 58 mph and above was in effect in the San Gabriels until 4 a.m. Friday and in the Antelope Valley until 10 tonight.
A less serious wind advisory will be in effect until 4 a.m. Friday on Santa Catalina Island, the Santa Clarita and San Fernando valleys, along the coast, and in downtown and the rest of metropolitan Los Angeles.
Along the coast, high surf is expected today, Friday and Saturday, and some flooding is possible, National Weather Service forecasters said.
"Minor coastal flooding is expected mainly in the vicinity of low-lying beaches and beach parking lots ... through Saturday morning," according to an NWS advisory.
A coastal flood advisory will be in effect through 11 a.m. Saturday along the coast from San Luis Obispo to Los Angeles, including around santa Catalina Island, with high surf and astronomical high tides expected to cause any flooding that occurs.
According to the NWS, approximate times for the high tides are 7:20 a.m. Thursday, 8:10 a.m. Friday, and 9 a.m. Saturday.
A coastal flood advisory indicates that winds and tides will combine to generate flooding along the coastline.
A high surf advisory, indicating an expectation of dangerous rip
currents and some beach erosion, will be in effect from noon today until 2 p.m.