DULUTH – The state's largest active wildfire grew substantially Friday, expanding to almost 13 square miles.

Late Friday, the Greenwood fire in northeastern Minnesota's Superior National Forest remained uncontrolled, and officials said it could threaten structures if overnight weather in the drought-hit area brings little rain, frequent lightning and winds gusting up to 50 miles per hour, as forecast.

Weather conditions are "the steering wheel and the gas pedal of the fire," Operations Chief Pete Glover said in a briefing Friday. "We're setting trigger points of when to move our crews back if the winds get too gusty and the fire behavior picks up rapidly."

The fire had grown to 8,215 acres by Friday evening as shifting winds and hot and dry conditions continued to ignite parts of the forest.

Earlier Friday, the fire spread across County Hwy. 2 in rural Lake County, prompting new evacuations in the Sand Lake and Stony Lake areas, according to the U.S. Forest Service.

More than 250 crew members are working the fire and will face "critical" fire weather this weekend, said Joanna Gilkeson, a public information officer for the Forest Service.

While the fire remains uncontained, no cabins or other buildings have been lost in the rural Lake County area, she said. But the fire is still a threat to a number of cabins, homes and recreational areas. One hundred such structures are in the evacuation area.

Structure protection includes brush clearing, creating space for crews to work and laying fire hose, with crews working day and night. They are continuing to create a barrier on the south end of the fire and find other areas to control the blaze.

On the north side, crews have started developing plans to "fight fire with fire" if needed near McDougal Lake, Glover said. Crews could intentionally start and control small fires to keep the wildfire from reaching unburned areas.

"For the most part the last week we've had southerly winds that are pushing the fire to the north and east," Glover said. "There is a front coming in with predicted winds switching to the west-northwest."

The fire, caused by lightning, was reported Sunday about 15 miles southwest of Isabella. Since then, the Lake County Sheriff's Office has evacuated 90 residences and notified 40 more they could be next as the fire moves closer to homes and cabins on its western side. Roads, campgrounds and recreational areas have been closed and a Red Cross shelter at the Finland Community Center has been established. Go to inciweb.nwcg.gov/incident/7805 for more information on the fire.

jana.hollingsworth@startribune.com 218-508-2450

brooks.johnson@startribune.com 218-491-6496