The first atmospheric river-fueled storm of the season is expected to make landfall in California on Wednesday afternoon, when it will dump inches of rain in the Bay Area, disgorge up to a foot of snow over the Sierra Nevada and likely trigger flash floods in fire-scorched wine country. The National Weather Service issued a flash flood warning from 4 p.m. Wednesday to 3 a.m. Thursday for those areas of Sonoma and Napa counties that were scorched by a multiple wildfires in October.