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GEYSERVILLE – The combination of wind and wildfire, they said, was creating a “worst case scenario,” as firefighters struggled to contain a growing blaze in the mountains of Sonoma County.

Tens of thousands of people packed up what they could and fled south. Mandatory evacuation orders expanded, then expanded again, until virtually half the county had been ordered to flee, emptying entire towns. Millions more braced for power outages across Northern California, then watched as their electricity was cut. Smoke drifted across the region, lending the skies an ominous haze.

By the end of the day, more than 90,000 people had been ordered to evacuate communities from the Mayacamas Mountains to the Pacific Ocean, out of fear that the Kincade Fire east of Geyserville could explode overnight, fueled by the strong, dry winds coming from offshore. Meanwhile, PG&E had begun cutting power to nearly 1 million customers across 36 Northern California counties — the largest intentional blackout so far.

Firefighters had hoped to get the upper hand on the Kincade Fire ahead of the winds that were expected to create extremely dangerous fire conditions beginning late Saturday. But the fire continued to grow: By Saturday evening it had consumed nearly 26,000 acres — about 40 square miles — and was only 10 percent contained.

The gusts were expected to pick up sparks and embers, carrying them ahead of the main blaze and starting new fires at a rate that could make efforts to douse the flames futile.

“You can’t fight a fire that is spotting ahead of itself a quarter of a mile, half a mile and in some cases a mile,” said Cal Fire Division Chief Jonathan Cox.

That fear, along with the memory of the panicked efforts to evacuate Santa Rosa neighborhoods as fires approached in 2017, prompted Sonoma County authorities to massively expand evacuation orders twice Saturday to cover all of Healdsburg, Windsor and Guerneville, plus other towns along the Sonoma Coast and the Russian River, as well as parts of Sebastopol.

The orders extended south to Santa Rosa, near the very neighborhoods that were devastated by the 2017 Wine Country fires. The Fountaingrove neighborhood was under an evacuation warning, with residents told to be ready to leave at a moment’s notice. Evacuation orders stopped just north of the Coffey Park neighborhood.

Sonoma County Sheriff Mark Essick called the orders the largest evacuation of the county in his 26-year career with the office.

“We want you to start evacuating now,” he said in announcing the Windsor and Healdsburg orders.

Authorities asked people to get out by 4 p.m. to give first responders time to prepare for massive wind gusts expected to pick up around 8 p.m., and to allow them to beat the power shutoff.

“Go means go,” Gov. Gavin Newsom said at a press conference late Saturday afternoon.

Restaurants rushed to pack up food that could spoil without power, while some residents climbed onto their roofs with garden hoses to try to protect their property. On Highway 101, cars packed with people, pets and possessions inched south toward Santa Rosa, while several columns of police vehicles rushed in the opposite direction, lights flashing.

Residents were sent to evacuation centers at the Santa Rosa Veterans Hall, the Petaluma Fairgrounds, and the Petaluma Veterans Hall. A shelter in Healdsburg, where about 90 residents fleeing Geyserville earlier this week were staying, was itself evacuated.

“We are really prioritizing safety right now for what is potentially the worst-case scenario,” Cox said. “This is the right thing to do.”

The North Bay and East Bay were under a red flag warning beginning at 8 p.m. Saturday and lasting till 11 a.m. Monday. The forecast called for 45 to 60 mph winds in the mountains with gusts up to 80 mph at the highest peaks. The coast and valleys, forecasters said, could see gusts up to 45 mph.

While winds that strong in 2017 lasted for about four to six hours, National Weather Service Meteorologist Steve Anderson said, “This time around we’re expecting winds that will last anywhere from 24 to 30 hours.”

A red flag warning will also apply to the Peninsula and the Santa Cruz Mountains from 3 a.m. Sunday to 11 a.m. Monday, when wind gusts are expected to hit 55 mph.

PG&E officials said the dangerous conditions forced them to shut off power across Northern California to avoid sparking another wildfire. Some 940,000 customers — well over 2 million individuals — were expected to lose power in 36 counties.

Taking no chances

A close call Friday evening underscored the danger of the Kincade Fire: A firefighter and two civilians were overcome by the fire during evacuations, but survived after taking cover in the firefighter’s emergency shelter.

In Lake County, the evacuations covered the communities of Adams, Anderson Springs, Cobb, Gifford Springs, Hobergs and Whispering Pines, as well as Ford Flat Road and Socrates Mine Road, according to Cal Fire.

Although in Healdsburg and Windsor, a handful of people chose to ignore the evacuation orders, the towns were still quiet and nearly deserted once the rush to get out had subsided.

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Dave Schlote’s wife told him about the evacuation order on Saturday and he rushed back from Napa to pick her up, along with their cat and some important documents and supplies from their home in Windsor, then drove to the Petaluma Veterans Hall. The couple had been watching the flames and smoke from a distance for the past couple of days.

“You have an understanding of just how quick it can change as far as the winds and the flames,” Schlote said.

He added that what happened to Santa Rosa in 2017 “could happen to us.”

Hundreds of cots were set up in the main auditorium of the veterans hall as people began arriving Saturday afternoon. A backup generator was in place for when the building was expected to lose power in PG&E’s shutdown, while volunteers set up air purifiers and waited for portable showers and extra bathrooms to arrive.

Jacob Fincher, 26, who has lived in Healdsburg his entire life, said this was the first time his neighborhood had been evacuated.

“It’s a little bit of a reality check,” Fincher said, as he packed food into the back of his pickup truck. “We’ve seen fires in the distance before, but never had anything like this.”

He and his family were going to a campground on the coast, hoping to get “as far as possible” from the fire. But possibly not far enough: An area stretching southwest from Highway 101 to the ocean was initially given an evacuation warning, which then changed to a mandatory order Saturday evening. On the Sonoma Coast, the evacuation order reached from Stewarts Point south to Bodega Bay.

The fire that prompted the evacuations ignited northeast of Geyserville late Wednesday. As of Saturday evening, the Kincade fire had destroyed 77 structures, including 31 homes, and was threatening more than 23,000 others, according to Cal Fire. There had been no reports of fatalities or missing persons.

The hilly topography east of Geyserville was contributing to the fire’s spread, Cox said.

The fire, he said, “heats itself up that mountain,” growing stronger on the way as it climbs.

“The task is monumental,” he said.

Reporters Joseph Geha and Jason Green contributed to this report.