Up to a foot of snow is expected to fall in parts of Southern California less than a week after the region experienced record-high temperatures.
A late season cold storm system will move into the region Wednesday night, bringing heavy snow to the mountains and rain to large cities like Los Angeles and San Diego, forecasts show.
The National Weather Service has issued a winter weather advisory from 11 p.m. Wednesday to 6 p.m. Thursday for communities surrounding the eastern San Gabriel Mountains, including Mount Wilson, Mount Baldy, Wrightwood and the Angeles Crest Highway, as well as Big Bear City and Big Bear Lake and other cities above the San Bernardino County Mountains.
The San Gabriel Mountains are expected to get the most snow -- with accumulations of up to 14 inches. Wind gusts as high as 45 to 50 mph are forecast, according to NWS.
MORE: California communities bracing for heavy flooding as record high temperatures melt record amounts of snowTravel could be "very difficult to impossible" on some of the mountain roadways, NWS said.
The unseasonable chilly weather began earlier in the week. Up to 7 inches of snow fell overnight Tuesday in the Sierra Nevada Mountains.
Rain will inundate much of the coast in lower elevations from San Francisco to Los Angeles. The Los Angeles hills could get up to an inch of rain.
The cool weather comes just days after the large parts of the West Coast experienced a heat wave with record-high temperatures.
MORE: California farming valley scrambles to save future as Tulare Lake floods take overThe soaring temperatures caused rapid melting of the snowpack that has accumulated this past winter. Some areas in California have received up to 221% more snowpack than average, according to the state's Department of Water Resources.
Officials are especially concerned about the agricultural lands surrounding the Tulare Lake Basin, which began flooding even before temperatures rose.
"There's nowhere else for this water to go in the Tulare Lake Basin," Daniel Swain, a climate scientist at the University of California, Los Angeles, said last week during an "office hours" session he streams on YouTube.
MORE: Flooding, mudslides possible as California snow melts amid another round of atmospheric riversAfter this week's cool down, temperatures are expected to continue to rise as summer nears, Swain said.
Last month, the California Department of Water Resources advised those living in snow melt areas to take steps to prepare for heavy flooding.
"Be aware of your flood risks, know where you're headed, know where your house or your business sits within or around potential for flooding," DWR officials said.