Firefighters expect to stare down hot, dry winds Friday as they battle the Glass Fire, which has consumed 61,150 acres in Napa and Sonoma counties.
The fire was 8% contained as of Friday evening, Cal Fire said.
A red flag warning for the North Bay mountains started at 1 p.m. Thursday and extends to 6 a.m. Saturday.; that makes it harder to fight the existing blaze, as well as increasing the danger of new fires igniting. Cal Fire officials have warned residents to be vigilant about calling in any new fires they spot.
A shift in winds is expected to push the blaze toward the southeast, in the direction of Angwin and Pope Valley, Cal Fire officials said. However, wind speeds are forecast to be between 15 mph and 25 mph, as compared to 50 mph winds that drove the fire southwest toward Sonoma County late on Sunday.
Temperatures in the upper 90s to, in the higher elevations and valleys, the low 100s are forecast for Thursday. Friday temperatures are forecast to be just slightly lower, according to the National Weather Service. If there is significant smoke, that could nudge temperatures down, the weather service said.
Also creating major challenges for the firefight is that the area the fire is burning in has not previously burned for at least 70 years, and has not been rained on for five months, Cal Fire analysts said.
That has led to a combustible mixture of grass, brush, hardwood and conifer timber that is critically dry.
The fire has destroyed at least 36 single-family homes in Sonoma County, along the eastern edge of Santa Rosa, and 107 homes in Napa County, according to Cal Fire's latest update Thursday morning.
While many evacuation orders or warnings in Santa Rosa and unincorporated Sonoma County have been downgraded of lifted, many areas of Napa County, including Calistoga and Angwin remain evacuated.