The National Weather Service on Wednesday warned residents of Los Angeles and Ventura counties to expect cold and windy weather with scattered showers on Thursday and Friday.
A cold, low-pressure weather system is combining with so-called "king" tides to increase flood danger along the California coast, forecasters said.
Daytime highs in the upper 40s and low 50s in most coastal and valley locations will be followed by subfreezing overnight temperatures through the weekend. Wind gusts could reach 25 mph on Thursday.
Normal average temperatures in the Los Angeles area for January are highs in the 60s, with lows in the mid-40s for coastal areas and low 40s in valleys, according to Joe Sirard, an NWS meteorologist.
"We're looking at temperatures dropping to at least 10 degrees below normal," Sirard said.
Top temperatures Wednesday in Los Angeles and coastal areas were in the high 60s and lower 70s. Temperatures are expected to drop to highs in the mid-to-upper 50s today before plummeting to the upper 30s or mid-40s overnight into Friday.
The San Fernando Valley will be slightly colder on Thursday, with highs in the upper 40s to mid-50s and lows in the upper 20s and mid-30s. Highs Friday are forecast in the mid-50s.
The coldest temperatures are expected Saturday morning as winds let up. Coastal valley low temperatures are predicted in the mid-20s in some areas, with a potential six hours of subfreezing weather threatening crops and garden plants.
Coastal temperatures on Saturday morning should dip into the low to mid-30s, with single-digit temperatures in some Antelope Valley spots.
Extreme cold and "dangerously low wind chills at times" are predicted for Southern California mountains, where icy roads and possible "black ice" will make driving extremely hazardous. Mountain highs are expected in the 20s and 30s.
The wind chill factor could be as low as 10 below zero in the mountains Thursday night into Friday morning and in the teens down to the single digits for interior valleys and the Antelope Valley.
There will be only slight improvement in temperatures overnight Sunday - two degrees at most. A slight warming trend is forecast early next week, with normal temperatures returning midweek.
Rainfall totals are expected to be light - a tenth of an inch or less in most areas.
The NWS reports that snow levels are expected to drop rapidly on Thursday, starting at 5,000 to 6,000 feet in the morning and dipping to 3,000 feet by the early afternoon. Snow levels could drop further into Thursday evening and Friday morning.
Less than 3 inches of snow is expected from the impending storm.
The extreme winter weather is being brought to Southern California by a very cold low-pressure system traveling in from the north early Thursday. Besides cold temperatures and scattered showers, strong winds out of the north will make it feel even colder.