ROCKY MOUNTAIN NATIONAL PARK, Colo. (CBS4) – The Fern Lake Fire has burned about 3,500 acres in Rocky Mountain National Park, and fire managers had big concerns about stronger winds Sunday night and Monday morning.

Wind gusts on Friday night with speeds as high as 75 mph stoked the fire, and evacuations were in place through the weekend. On Sunday about 681 evacuations remained in place. That was a lower number than on Saturday because the fire is so far contained to within the park boundaries. The official number on containment on the fire during the day on Sunday was 20 percent.

The new concern is that a repeat of what happened Friday night could happen again, and the fire could be pushed further east in the direction of Estes Park.

“At around 11 p.m. winds could drop down into this area in the 60 to 70 mph range from the west, which is conditions similar to what we had Friday night when this fire moved three miles in 45 minutes,” Park Ranger Larry Frederick told CBS4.

Evacuees and concerned residents were briefed on the details of the firefight Sunday night. The evacuation center is at the Mount View Bible Fellowship Church.

“This is an area that is not necessarily prone to fire, but yet with the climatic changes we’ve been experiencing and the weather patterns we’ve been experiencing, occasionally we get these large, disruptive fires,” Frederick said.

Fire manager Traci Weaver points to a map showing the Fern Lake Fire boundary. (credit: CBS)

Firefighters on Sunday cleared brush outside the Moraine Park Visitor Center just in case wind-blown embers would approach the historic building.

Frederick said the National Park Service has deep concerns about the fire’s impact. The park’s Beaver Meadows entrance on the east side is currently closed to visitors.

“It’s upsetting that it’s creating so much havoc in the park. It’s upsetting that it’s affecting visitor use of the park, and it’s extremely upsetting that it’s affecting the town of Estes Park, our residents,” he said.

The fire has been burning since Oct. 9. It’s believed to have started from an illegal campfire.

So far no air tankers have been able to get involved in the firefight due to the gusty conditions.