The first big storm of autumn will arrive in San Diego County Wednesday night and drop between one-half and one inch of rain along the coast and upwards of 2 inches in the mountains, where strong winds will blow, according to the National Weather Service.

An inch or more of rain is expected in the county’s inland valleys and foothills.

Forecasters say the system will swirl ashore from the North Pacific and drench the region well into Thursday, possibly causing flash flooding. The rain also could cause debris flows in the areas of Los Angeles and Ventura counties that were recently hit by major wildfires.

Snow could fall as low as the 6,500-foot level, and six inches of snow could blanket mountains above 7,000 feet.


Forecasters also are expecting large surf at the coast.

Downtown San Diego hasn’t received an inch or more of rain in a single day since January, and the landscape is critically dry. Forecasters expect weak offshore winds through Tuesday, ahead of the storm.