Flood advisory issued for Napa and other Bay Area counties

The National Weather Service issued a flood advisory Sunday morning for Napa, Marin, Sonoma, Alameda, Contra Costa, San Francisco, San Mateo and Santa Clara counties.

A flood advisory indicates that what the NWS calls "nuisance flooding" is underway or expected to occur.

The advisory is in effect until 9:30 p.m. It warns that "at 6:24 a.m., automated rainguage and Doppler radar data indicated ... rain rates have been sufficient enough to produce ponding on the roadways."

The ponding and localized flooding could persist after the rain has stopped, particularly in low-lying areas and those with poor drainage, the advisory continues.

This weekend's heavy rainfall is also expected to raise the water levels in small creeks and streams, some of which may overflow, according to the NWS. 

At 8:30 a.m. Sunday, the level of the Napa River at Lincoln Avenue in Napa had risen 1.25 inches in 24 hours, according to sensor data from the Napa Valley Regional Rainfall and Stream Monitoring System.

However, the river level was still less than four feet; monitor stage is 16.5 feet and flood stage is 18.5 feet.

The  will make sandbags available free of charge if the National Weather Service issues a flood watch or flash flood watch for the Napa River and/or its tributary creeks in and around the city. Check the city's home page, cityofnapa.org, for updates.

In the mean time, the NWS is cautioning travelers to leave extra time to reach their destinations and to beware of flooded roads.

"If water covers the roadway do not cross it. The water may be too deep to allow your vehicle to cross safely," the flood advisory warns.

Along with heavy rainfall at times, the week ahead may include thunderstorms and even hail, according to the National Weather Service forecast.