A wildfire in Shenandoah National Park nearly doubled in size on Tuesday, thanks to strong winds and low humidity. The National Park Service says the blaze, named the Rocky Mount fire, has charred 4,000 acres — up from a little over 2,000 acres on Monday night.

“I can speak with full confidence that the structures around the park are protected,” said John Miller, the Virginia Department of Forestry state wildland fire chief, but the National Park Service has fire suppression responsibility within the park itself.

Miller says the Virginia Department of Forestry has been creating fire lines with bulldozers to prevent it from spreading. “Dozer lines,” as they’re called, are created using a bulldozer to dig out the flammable vegetation. What’s left behind is a wide line of dirt that the fire cannot easily spread beyond, though particularly intense fires in very windy conditions can often jump these lines.

On Monday, the department put in dozer lines on the east side of the fire to protect homes in Beldor, Va. But a wind shift was in the forecast, and they knew that the western side of the fire would also soon be at risk. Tuesday they focused on creating lines on the west side to protect structures and subdivisions along U.S. Route 340.

“So now we’ve got an easterly wind, which pushes the fire back west,” Miller told The Washington Post on Wednesday. “So if we didn’t have a line in place the fire would have been blown into those structures.”

Miller says now it’s up to the National Park Service to contain the fire on the south end.

A wildfire burning in Shenandoah National Park has burned more than 4,000 acres. (Twitter/ @FratBasterd)

About 250 people are working to control the Rocky Mount fire within Shenandoah National Park, the National Park Service told The Washington Post. This includes personnel from the park service, the Virginia Department of Forestry, the agriculture department and others. Major highways, visitor facilities in the park and nearby communities remain open, the National Park Service reports on its website.

Skyline Drive remains closed between mile 65, around Swift Run Gap, and mile 79, Loft Mountain. The closure of the Appalachian Trail has grown to 12 miles between Powell Gap and Doyles River Overlook. The National Park Service reports 13 other trail closures in addition to the Appalachian Trail.

The majority of the fire is burning in Rockingham County, Va., though smoke has wafted southeast over the past few days, creating a brown haze across parts of central Virginia. Authorities are asking people to only call 911 if they actually witness a fire burning, NBC29 reports.

Although weather has been uncooperative over the past couple of days, conditions are improving, says National Weather Service fire weather forecaster Andrew Woodcock. He noted that the shape of the smoke plume on satellite suggested winds were improving.

“The last couple of days the smoke has been sort of like a flashlight beam in Rockingham County. There was a pretty fine line of smoke that has been trailing southeast of the fire,” Woodcock said. This indicated that strong winds were in place over the wildfire. “Today [the smoke] is more diffuse. The winds are definitely not as strong today as they’ve been previous days.”

Rain is possible Thursday night into Friday, although it probably won’t be enough to put out the fire. Just a half-inch of precipitation is expected through Friday night. A potentially windy Saturday could be problematic if the fire is still burning at that point, Woodcock said.

“We are stationing people around the fire and putting in containment lines, the Virginia Department of Forestry is putting in a dozen lines in various places around the fire, and we’re just trying to hold it in the park,” Sally Hurlbert, a ranger with the National Park Service, told NBC29 in Charlottesville, Va. “We won’t let it get out of the park.”

Officials don’t know what sparked the fire on Saturday, but they think it was likely human-caused.