LOS ANGELES (CBSLA) — The first major rainstorm of the fall season reached the Southland late Tuesday night, producing moderate to heavy precipitation in some areas of the Inland Empire, prompting road closures.

At about 11:30 p.m., Caltrans tweeted that the eastbound lanes of the 10 Freeway at Apache Trail in Riverside County were closed due to flooding. Over in San Bernardino County, State Route 62 at mile marker 125.65 was also closed due to flooding.

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Shortly before 4 a.m., all eastbound lanes of the 10 Freeway at Apache Trail in Riverside County were reopened, according to Caltrans.

The National Weather Service issued a flash flood warning for San Bernardino and Riverside counties  and the northeastern portion of Imperial County that expired at 4 a.m. Wednesday. The warning said small creeks and streams, urban areas, highways, streets and underpasses as well as other drainage and low-lying areas could be affected by flood waters.

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Forecasters said the most significant rainfall was expected throughout Wednesday and in the early morning hours of Thursday, with the season’s possible first snow in the mountains.

“Rainfall totals through Thursday could range from 0.5 to 1 inch near the coast, to 1.5 to 2 inches in the mountains, with less than .25 inch in the deserts,” according to an NWS statement. “The snow level will lower to around 6,000 feet for Wednesday through Thursday, with a few inches of snowfall possible in the mountains of San Bernardino and Riverside counties above 6,000 feet.”

To prepare, the Los Angeles Department of Water and Power has deployed K-Rails in burn scar areas to help prevent dangerous mudslides from entering roadways. In response to the Palisades Fire, 47 K-Rails were installed in late October near the intersection of Sunset Boulevard and Palisades Drive. Another 50 K-Rails have been installed along Sepulveda Boulevard in response to the Getty Fire. K-Rails still remain along La Tuna Canyon Road from the La Tuna Fire two years ago and in the Lakeview Terrace area from the Creek Fire, also two years ago.

A winter storm warning was set to go into effect at 7 a.m. Wednesday through 7 p.m. Thursday for the San Bernardino and Riverside county mountains including the cities of Lake Arrowhead, Big Bear City, Big Bear Lake, Running Springs, Wrightwood and Idyllwild-Pine Cove. According to the NWS, heavy snow was expected with total snow accumulations of 4-8 inches for lower elevations and up to 10-14 inches or more for elevations above 7,000 feet.

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Thunderstorms were also in the forecast, as well as strong winds, as atmospheric instability was set to increase as the tropical storm system from the south clashed with a polar storm system from the north.