The Dixie Fire exploded in size again this week, spreading across nearly 275,000 acres of the northern Sierra and forcing new evacuations as the fight against California’s largest wildfire of the season continued into its third week.

Unpredictable weather — coupled with the fire’s massive reach across steep canyons and remote forestland in Butte and Plumas counties — has made it difficult to predict how and when crews might get the upper hand on the erratic blaze, firefighters said. The blaze — which has threatened small communities and popular vacation spots including around Lake Almanor — now ranks as the eighth-largest wildfire on record in the state.

“I don’t really have a ton of feel for what this thing is gonna do beyond the next couple days,” said Cal Fire spokesperson Rick Carhart. “This fire is just so huge.”

Smoke blowing from wildfires raging across Northern California was expected to reach the Bay Area on Wednesday, with an air quality advisory issued for the North and East Bay through the rest of the week. Fires burning across Siskiyou, Shasta and Trinity counties could create unusually hazy skies, but air quality was forecast to remain in healthy ranges, the Bay Area Air Quality Management District said.

Hot, gusty winds and unburned fuel meanwhile sparked fresh flames in the Dixie Fire through Wednesday, according to Cal Fire. To the northeast, wind-blown embers spawned spot fires outside the blaze’s main body starting Monday afternoon. Harsh winds were expected to lead to more unpredictable spotting throughout the rest of the week.

“With it being so hot and dry, basically almost every ember that lands on the grass is igniting and catching on fire,” Carhart said. “That’s the concern.”

The National Weather Service issued a Red Flag warning for much of northeastern California for Wednesday and Thursday. During that time, wind gusts could range between 30 and 40 mph and push the fire further north into the Highway 89 corridor, said NWS meteorologist Ryan Walbrun.

Humidity will meanwhile hover in the “critically dry” single digits, making it difficult for firefighters to gain any traction overnight when humidity typically rises.

“Up above the fire itself, it’ll be very unstable, very windy conditions,” Walbrun added.

Gusts are expected to ease of Thursday and Friday but then switch directions to push the fire to the southwest.

Five thousand firefighters are battling the blaze and are expected to spend the rest of the week defending virtually the entire west shore of Lake Almanor, a popular vacation destination dotted with multi-million-dollar homes and smaller communities. To the southeast, the Bucks Lake Wilderness area has also emerged as a key defense point in the fire fight.

Officials warned that unburned fuel inside the fire’s interior — along with wild winds high above the flames — will lead to billowing smoke clouds across the two counties, particularly as new spot fires break out and potentially spread.

“We expect it to be very intense again,” CalFire Battalion Chief Mike Wink said of the fire activity.

The Dixie Fire has been burning for just over three weeks after breaking out in mid-July northeast of Paradise. Since then, it has surged in fits and starts — until the last few days, when the dip in humidity and rise in winds helped it make worrisome runs near Highway 89.

PG&E has alerted regulators that two separate equipment malfunctions may be linked to the Dixie Fire and the Fly Fire, a 4,300-acre blaze in Plumas County that merged with Dixie about two weeks ago.

As of Wednesday, the Dixie Fire was about 35% contained and had destroyed 67 structures.