Firefighters in Sonoma and Napa counties are bracing for two days of bigger and faster flames as high winds return, but containment on the Glass Fire inched up overnight to reach 5 percent.

The fire straddling both counties grew by around 5,500 acres last night to a total area of 56,781 acres, or 89 square miles.

Heat will play a role in the firefight over the next few days, as triple-digit temperatures have been predicted in addition to an uptick in dangerous, gusty winds in the North Bay hills. Fire crews continue to dig fire breaks using bulldozers and hand tools, and so far they have slowed the fire's spread to the west and south. The northern section of the fire in Napa County continues burning actively in Robert Louis Stevenson State Park.

via #Firemappers

A Red Flag Warning that was issued Wednesday, beginning on Thursday afternoon at 1 p.m., has now been extended through 6 a.m. Saturday.

As was forecast on Wednesday, winds are expected to pick up out of the northwest, with gusts up to 30 miles per hour at higher elevations. This is expected to potentially change the course of the firefight and increase the size of the Glass Fire, though maybe some existing containment lines will hold.

The direction of the wind is, at least, expected to push the fire away from eastern Santa Rosa, which was under threat on Sunday night.

The fire has primarily been burning, on the Sonoma side, between the burn scars of the 2017 Tubbs and Nuns fires, and in an area of Napa County that has not recently burned, outside the lines of the LNU Complex.

"The area where the fire is burning has no fire history over the last 70 years," said Cal Fire Fire Behavior Analyst Brian Newman, speaking to KPIX. "It’s led to an excessive build-up of fuel — heavy, dense brush... There’s really no [natural] barrier to burning."

As KPIX reports, Governor Gavin Newsom was expected to be touring some of the fire area on Thursday, and meeting with impacted residents.

The fire has destroyed at least 143 homes as of the current count. So far, no casualties have been reported in connection with this fire.