The first of a pair of storms pounded Northern California on Thursday, bringing heavy bands of rain to the North Bay, causing minor flooding and mudslides, and raising the specter that the flood-prone Russian River might spill its banks.

The National Weather Service’s hazardous outlook remained in place for the most of the Bay Area as on-and-off downpours were forecast to continue Friday. Parts of Sonoma and Napa counties were expecting as much 4 inches of rain by Friday evening, igniting fear that a region thirsty for rain might get too much too fast.