LOS ANGELES — Rain fell on the Southland early today as a result of the first of two storms forecast to strike the region, and forecasters said the second system would make travel conditions through the San Gabriel Mountains exceedingly challenging.

Rainfall totals ranging from a tenth of an inch to a half-inch are expected across Los Angeles and Ventura counties, with up to an inch in the eastern San Gabriel Mountains and foothills, as a result of the first storm, which arrived yesterday packing an infusion of moisture from south of Los Angeles and which is forecast to clear out by this afternoon, National Weather Service forecasters said.

“Another more dynamic storm system is expected to move down from the Gulf of Alaska and approach the forecast area by Friday afternoon. There could be some light rain ahead of the main storm system, but expect moderate to locally heavy rain Friday evening through the overnight hours,” warned an NWS statement, adding that the rain will turn to showers by early Saturday morning.

The second storm, which originated to the north in the Gulf of Alaska, is expected to produce from a half-inch to an inch of rain in coastal and valley and between one and two inches in the San Gabriel Mountains, the statement said.

“There will likely be some local urban flooding with this system and the possibilities of mud and debris flows across recent burn areas,” it said.

Also, “Gusty winds will make driving difficult, especially for drivers of high-profile vehicles,” warned an NWS statement, advising extra caution. “The gusty winds will also cause downed trees and could cause power outages.”

In the San Gabriel Mountains, heavy precipitation is expected starting Friday afternoon, turning to showers by Saturday morning, which will continue through Saturday night, according to an NWS statement. Snow levels will be at between 5,000 and 6,000 feet Friday, then drop to between 3,000 and 4,000 feet by Saturday morning, it said.

“If this occurs as expected, it would severely affect travel into or through the mountains, even on heavily travelled Interstate 5 during the holiday weekend,” the statement said.

The NWS said there is the potential for snow accumulation of 8 to 16 inches above 6,000 feet, 4 to 8 inches between 4,000 and 6,000 feet, and between 2 and 4 inches between 3,000 and 4,000 feet and across Interstate 5 from the Gorman area to The Grapevine.

Also expected in the San Gabriels are strong, gusty winds — 25 to 35 mph, with 60-mph gusts — which will create areas of blowing snow, reducing visibility to zero at times, forecasters said. Combined with temperatures in the 20s and 30s, the winds will also “create dangerously low wind chill values” through Saturday night, a statement said.

Given these conditions, a winter storm watch will be in force in the San Gabriels from Friday afternoon through late Saturday night.

The NWS forecast showers today in L.A. County and highs of 58 degrees Fahrenheit in Palmdale; 59 in Lancaster; 60 on Mount Wilson; 64 in Avalon and Saugus; 67 in Long Beach, San Gabriel, Burbank and at LAX; 68 in downtown L.A. and Pasadena; and 70 in Woodland Hills.

Friday’s L.A. County forecast calls for rain and highs 5-6 degrees lower than today, followed by showers and temperatures in the 50s on Saturday, then partly cloudy skies and temperatures back in the low 60s on Christmas Day.

A combination of showers and partly cloudy skies was forecast in Orange County today, along with highs of 63 in Laguna Beach; 64 in San Clemente; 65 in Newport Beach, Mission Viejo and Yorba Linda; and 66 in Fullerton, Anaheim and Irvine.

Friday’s forecast in Orange County envisions cloudy skies Friday and highs only marginally lower than today’s, followed by rain and highs in the mid to high 50s Saturday and sunny skies, with temperatures in the high 50s and low 60s on Christmas Day.