What to Know
The brunt of the storm is expected Friday afternoon
Rainfall records are likely across the region
The system is expected to move out late Saturday
Flash flood watches are in effect Thursday ahead of the season's strongest storm, a two-day soaker that will boost rainfall totals during what has already been one of California's wettest winters in years.
About 2 to 6 inches of rain are likely from the Southern California coast to the valleys by Saturday night. Showers are expected to begin late Thursday before the full force of the storm is unleashed midday Friday and into Saturday.
"This will likely go down in the record books as one of the wettest February days ever," said NBC4 forecaster Crystal Egger.
Some communities could see a month's worth of rain in one day during what is expected to be the region's most powerful storm of the wet season -- October through April. The system is the product of an atmospheric river, tropical moisture that flows north to the West Coast, ushering in waves of precipitation that can go on for hours.
The steady rainfall brings concerns about landslides in the region's burn areas, particularly in the San Gabriel Valley and mountains east of Los Angeles, due to unstable soil. Four to 8 inches on rainfall are possible in the mountains and foothills.
A flash flood watch will be in effect from Friday morning through Saturday morning. Widespread roadway flooding is also possible, along with flooding in creeks and small streams, and rock and mudslides, especially near canyon roadways.
Officials with the city of Duarte declared a "red alert" for residences in the Fish Fire burn area. The alert means mandatory evacuations will go into effect at 7 a.m. Friday morning, depending how the storm develops. An evacuation center will be established at the City Hall Community Center, 1600 Huntington Drive.
Evacuations also are possible due to mudslide concerns in Glendora and Azusa beneath the Colby Fire burn area. Azusa officials have been distributing sandbags to residents at the City Yard, 809 N. Angeleno Ave.
Los Angeles County Public Works crews, meanwhile, worked frantically to clear debris from catch basins and storm drains in hopes of preventing flooding.
In the mountains, heavy snow is expected at higher elevations, along with gusty, damaging 70-mile-per-hour gusts. The snow level will vary from as low as 6,000 early Friday to 8,000 feet Friday night, then fall back to 6,000 feet. A winter storm warning will be in force in the San Gabriel mountains from Friday morning through Saturday morning.
Between 1 and 2 feet of snow are possible above 8,000 feet and between 6 and 12 inches above 6,000 feet.
The storm marks the latest bout of rainfall during what has been the wettest winters in years. Normally, downtown Los Angeles would have received 8.96 inches of rain by this time of the year in the season that runs from October to April, but it already has had 16.25 inches.
The steady stream of storms have knocked out drought conditions across Northern California. Last year at this time, 95 percent of California was in drought. That figure was at 24 percent Thursday, according to the U.S. Drought Monitor report.