An unseasonably cold storm that originated in the Gulf of Alaska will bring the Southland periods of rain and snow today and Friday, along with fierce winds, creating dangerous driving conditions in the San Gabriel Mountains and the Antelope Valley, National Weather Service forecasters said.
Steady rain linked to a weakening cold front will move into San Luis Obispo and Santa Barbara counties this morning, then dissipate, according to an NWS statement. The remains of the same front will create a slight chance of showers or drizzle in Ventura and Los Angeles counties, it said.
This afternoon, a cold and unstable air mass will slide into the Southland, this time likely bringing showers, along with a slight chance of thunderstorms, the statement said. Then, a second impulse will materialize tonight and Friday, likely mostly missing San Luis Obispo and Santa Barbara counties but affecting Los Angeles and Ventura counties by generating showers and a slight chance of thunderstorms, it said.
Any thunderstorm that develops will pack the potential to produce brief, heavy rain, gusty and erratic winds, small hail, dangerous cloud-to-ground lightning, and even isolated waterspouts, according to the NWS statement.
Most areas will receive between a quarter-inch and three-quarters of an inch of rain, the statement said. But in the San Gabriel Mountains and foothills and near where any thunderstorm shows up, up to an inch-and-a-half of rain is possible, it added.
The potential for heavy showers resulting from a thunderstorm creates the possibility of minor debris and mud flows over slopes previously denuded by wildfire, the NWS said, describing a threat to communities below the foothills of the San Gabriel Mountains.
In Glendora, local officials raised the alert status to “yellow” for residents living below the Colby Fire burn area. The yellow status requires residents to remove vehicles, trash containers and other obstacles from streets to protect against damage from possible flooding or mud flows and to ensure emergency crews can access the area.
In the San Gabriels, the snow level will drop to around 6,000 today, then to around 5,500 feet tonight and Friday, the NWS forecast, adding that between three and six inches of snow is expected to accumulate between 6,000 and 7,000 feet.
Also expected are strong gusty winds, which will churn up blowing snow and make driving in the mountains hazardous, forecasters said. A winter weather advisory, which is issued to herald dangerous driving conditions, will be in effect in the San Gabriels from 3 p.m. today until 8 p.m. Friday.
The winds are also expected to lash the Antelope Valley, where a wind advisory will be in force from 10 a.m. today until 10 p.m.
Forecasters said that from this morning until tonight the Antelope Valley will experience southwest winds blowing at sustained speeds of between 20 and 30 miles per hour and gusting at 45 mph, and at as much as 55 mph in foothill areas such as Poppy Park and Lake Palmdale.
Crosswinds and blowing sand and dust may affect road travel in the Antelope Valley, restricting visibility, especially on the Antelope Valley (14) Freeway and Pearblossom Highway (state Route 138), they said.