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An atmospheric river is expected to bring heavy amounts of moisture to the region, with up to two inches falling in some areas by the time the weekend arrives. Here's everything you need to know.
When will the rain hit Southern California?
Showers moved into the greater Los Angeles area around 11 p.m. Wednesday and heavy rain began around 6 a.m. Thursday. By 8 a.m. Thursday, the storm is expected to move into Orange County and the Inland Empire. Forecasters said rain could fall at a rate of a half-inch per hour, with some isolated areas seeing a rate of three-quarters-of-an-inch per hour.
Then by 2 p.m. Thursday, the rain is expected to turn into scattered showers.
"This first system is a fairly quick moving one but has a strong upslope component that will enhance rain rates, especially in the foothills and mountains," according to the National Weather Service. "But models also indicate some instability with this system so isolated thunderstorms are possible, especially over and near the coastal waters.''
By Friday and Saturday, it is expected to be mostly dry with some lingering showers.
"So there will likely be typical roadway flooding across the area but overall not expecting any significant flooding problems,'' according to the NWS.
Which areas of Southern California see rain?
Los Angeles County weather
This area began to see showers come in late Wednesday night (after midnight) with about 1 to 2 inches of rain in areas like downtown and East L.A. Then, the rain will intensified Thursday morning.
Also, a high surf advisory will be in effect from 2 a.m. Thursday through 6 a.m. Saturday, with west-facing beaches possibly seeing waves peaking at 8 to 12 feet.
Orange County weather
Widespread rain is also expected in Orange County, where forecasters issued a flood watch that will be in effect from Thursday morning through Friday morning. A high wind watch will also be in effect on Thursday, while a high surf advisory will be in place from 2 a.m. Thursday through 6 a.m. Saturday.
Forecasters said Orange County beaches could see waves of 4 to 6 feet, with some as high as 8 feet.
Weather in the valleys and the Inland Empire
Heavy rain is expected in these areas Thursday with rainfall totals likely to range from 2 to 4 inches.
Mountain communities weather
Snow levels will drop to about 6,000 feet by Thursday afternoon, with "several inches of snow'' likely in higher elevations. Strong winds will also accompany the storm system, with gusts up to 50 mph possibly in mountain areas.
A winter storm watch will be in effect from late Wednesday night through Thursday evening in the San Gabriel Mountains and in the 5 and 14 Freeway corridors. Forecasters said up to 12 to 24 inches of snow could fall above 7,000 feet, with 6 inches possible at 6,000 feet 1 to 4 inche at 5,000 feet.
When will the rain end?
For now, Southern California will get less of a chance of rain on Saturday but don't put away the umbrellas. There's also rain on the forecast for the weekend.
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Is there a second storm?
A second storm will begin moving into the Southern California region Sunday afternoon and will stick around until Tuesday, possibly Wednesday.
The storm will begin a "lengthy storm cycle'' that could bring widespread rain totals of 2 to 4 inches in lower elevations, and possibly twice as much in south-facing mountains. It could also cause flooding and mudslides.
City News Service, Inc. contributed to this report.