Red flag warning issued for SF Bay Area: What you should know

A fire weather watch for the Bay Area was upgraded to a red flag warning on Friday as confidence in the forecast is high that dangerous conditions that allow wildfires to spread easily will develop over the weekend, the National Weather Service said. 

The warning was split into two segments: The first includes elevations above 1,000 feet and starts at 5 a.m. Saturday, and the second covers elevations below 1,000 feet and begins at 5 p.m. Saturday. Both run until 5 p.m. Sunday. “Most critical time period will be Saturday night through early Sunday morning,” Matt Mehle, a meteorologist with the weather service, wrote in a message. “Wind Advisory also remains in effect Saturday morning through Sunday evening.”

The weather service’s Bay Area office issued a map showing which portions of the region will fall under the warning. The Sacramento office, which forecasts weather for Solano County that’s part of the Bay Area, also issued a map.

There are two levels of fire weather warnings. A fire weather watch is issued up to 72 hours before dangerous fire conditions could possibly develop, while a warning is issued about 24 hours before there’s a high likelihood of conditions developing that promote wildfire spread, according to the weather service. 

Late summer and early fall rains have helped prevent wildfires in California in recent weeks, but the impact of the moisture is waning. “The more dense fuels such as larger trees are still holding onto some moisture from the recent rains,” Dalton Behringer, a forecaster with the weather service, said. “It’s the finer, flashier fuels such as grasses and shrubbery that we’re more worried about.” 

Northerly winds are expected to pick up early Saturday morning across the ridges of the North Bay, East Bay and the Santa Cruz Mountains. The winds are forecast to peak late Saturday into Sunday morning, with sustained winds up to 30 mph likely and isolated gusts up to 70 mph possible on the highest peaks, the weather service said.

Humidity levels could drop to 10% to 25% across the Bay Area on Sunday.