More than 100 firefighters worked overnight — and in the face of shifting winds — to battle the 300-acre Flagstaff Fire and to prevent it from spreading into the city of Boulder.

A federal Type 1 team, which was pre-positioned in Jefferson County, is expected to arrive Wednesday morning to defend against the wind-whipped wildland fire that was sparked early Tuesday afternoon.

Daytime firefighting efforts in upper Skunk Canyon were led by an air assault, including a massive C-130 air tanker dropping slurry. Shifting winds moved the fire north, south and east, delaying initial efforts for a ground attack, said Kim Kobel, Boulder police and fire spokeswoman.

The fire was burning in unpopulated, rough terrain, with spotting out in front of the blaze.

“The fire is burning in several directions at once,” Kobel said.

A task force of 40 firefighters from the Boulder Fire Department was sent to create defensible lines and check on the spot fires, visible from Boulder on the ridge behind the National Center for Atmospheric Research.

The spot fires were about a quarter-mile ahead of the Flagstaff Fire, which had not jumped the ridge, said Boulder County Sheriff’s Cmdr. Rick Brough.

As of Tuesday night, the fire continued to burn with no containment, however no structures were threatened, Brough said. Nearly 30 homes were evacuated along Flagstaff Road and Bison Drive, he said.

“We’re about one ridge over from the city of Boulder,” Brough said.

An update late Tuesday night from the Boulder Office of Emergency Management warned of increasing winds Wednesday.

“Favorable weather conditions overnight are expected to keep fire activity low,” the 11:30 p.m. update said. “However, hot temperatures and increased winds predicted for Wednesday could increase the movement and intensity of the fire tomorrow.”

Bill Holmes and his wife, Glenda, were among the first people to spot the fire. Their home on Bison Drive was less than mile from the flames when they evacuated, he said.

“When it was really raging, the wind was probably blowing at 25 miles per hour at least,” Bill Holmes said. “(The fire) went straight up the hill on South Boulder Peak.”

Pre-evacuation orders went out to 2,416 south Boulder phone numbers in the neighborhoods of Table Mesa, Devil’s Thumb and Highland Park, which are bordered by Dartmouth Avenue to the north, Greenbriar Avenue to the south, Broadway to the east and the foothills to the west.

Flagstaff Road was closed to all non-emergency personnel. NCAR on Table Mesa Drive just west of Boulder also elected to evacuate Tuesday.

The evacuation center at East Boulder Recreation Center, 5660 Sioux Drive, remained open overnight.

Kobel urged residents in the pre-evacuation areas to be “ready to move, if necessary,” cautioning that the unpredictable weather and wind conditions combined with dry terrain created a very combustible situation.

“Conditions are at some of the most extreme levels we’ve ever seen in Colorado,” she said.

The fire started near the 1500 block of Bison Drive in the Walker Ranch area around 1:15 p.m. and was believed to have been sparked by lightning, although an official cause has yet to be determined, Brough said. At least four other small grassfires were reported after the early afternoon thunderstorm.

The other fires were stamped out, but the Flagstaff Fire shot up through the rugged terrain. Given the placement of the fire and the winds, the first attack on the blaze came from the air by helicopters, air tankers and planes.

By Tuesday evening, about 200 firefighters from 11 agencies were working the fire, and crews were assembling at Fairview High School in case the wildfire burned into the city.

“This is the structure protection plan,” said Jeff Long, battalion chief for Boulder Fire Rescue. “We are staying here in case it takes a turn for the worse. As long as the city is threatened, we’ll be here.”

Camera Staff Writer Joe Rubino contributed to this report.

Contact Camera Business Writer Alicia Wallace at 303-473-1332 or wallacea@dailycamera.com.