Amid the relentless rain brought by an atmospheric river soaking Northern California, a flash flood warning was issued Friday afternoon for San Francisco and parts of San Mateo County where instances of flooding deemed "life-threatening" were occurring.

A powerful atmospheric river storm that drenched the North Bay for two days in a row and set rainfall records moved south Friday, bringing steady rain starting around mid-day that was expected to soak the entire Bay Area until Saturday morning.

An atmospheric river that has brought damaging wind, rain and snow to the Pacific Northwest fed a storm spreading as far south as Los Angeles.

A third day of an atmospheric river storm has inundated Northern California and the Bay Area, with the storm spreading from the North Bay south across the region, flooding creeks, roads, and low-lying areas.

The National Weather Service on Friday issued several flash flood warnings in parts of the Bay Area as heavy rain saturated the region.