LOS ANGELES - On the heels of a warm and sunny stretch, a "massive cool down" will begin around the Southland Thursday, along with rain and mountain snow.
A pair of weather systems are bearing down on the region, with the first expected to arrive Thursday, and wet conditions likely to continue through Saturday.
"Clouds will be on the increase on Thursday and there will be a massive cool down," according to the National Weather Service. "Rain is likely Thursday night and Friday morning, along with mountain snow and a slight chance of thunderstorms."
Forecasters said a second, colder system will move in Saturday and continue into the evening, bringing "another chance of showers to the area."
Thursday's initial cold front will bring cloud cover to the region and drive down temperatures, with rain developing first along the Central Coast, moving into Los Angeles County by Thursday evening. The rain will taper off later Thursday evening and Friday morning, although some lingering showers are possible Friday afternoon.
Rainfall totals are supposed to be relatively low, with most areas receiving a quarter- to three-quarters of an inch of rain, although the San Gabriel Mountains could get slightly more, forecasters said. There will be a slight chance of thunderstorms developing, possibly resulting in "brief heavy downpours and small hail." Snow levels will drop to 4,500 to 5,000 feet Thursday evening, with 5 to 10 inches of snow possible at higher elevations, according to the NWS.
The storm will lower temperatures by about 8 to 12 degrees Thursday, and another 5 to 10 degrees on Friday, when temperatures will average about 10 degrees below normal, forecasters said.
Another cold front is expected to arrive by Saturday, bringing another chance of showers and more snow in the mountains. The snow level could drop as low as 3,000 feet, and temperatures will fall a few more degrees, keeping most of the region in the mid to upper 50s.
A winter storm warning will be in effect for the Los Angeles County mountains, excluding the Santa Monica range, through Sunday morning.
"Plan on slippery road conditions," forecasters warned. "Road closures are possible during this event, including Interstate 5 over the Grapevine, Highway 33 through the Grapevine and Highway 2 through the San Gabriel Mountains. Roads may remain icy and impassable well after snowfall has ended."
Forecasters said conditions should begin to rebound on Sunday with clear skies. Warmer weather is expected to return by Monday.
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