The Arnica Fire was ignited by lightning on September 13 and detected on September 23 in the Arnica Creek area north of West Thumb and southwest of Dryad Lake in Yellowstone National Park. The fire was 4 acres on September 23, then with warm, dry, windy weather grew to 250 acres on September 24 and to 1,600 acres on September 25. With warm windy conditions continuing on September 26, the fire moved eastward and grew to 8,300 acres. The fire increased an additional 1,000 acres on September 27 but did not grow significantly on September 28. It is now estimated at 9,300 acres.

Fire personnel are managing the fire for multiple resource objectives, allowing the burn to progress naturally in areas where ecological benefits can be achieved, while using helicopters to cool portions of the fire perimeter nearest values at risk. Structure protection measures, such as clearing brush around buildings and setting up hose lays and sprinkler systems, are in progress at Bridge Bay and Lake Village.

The Grand Loop Road between Fishing Bridge Junction and West Thumb Junction is closed indefinitely due to active fire on both sides of the road and falling burned trees. Firefighters are working to remove fallen trees from the roadway, but more continue to fall as the fire actively burns in the area.

Park visitors are reminded that the Lake Village area, including the Hotel and Lodge, remains open and is accessible from the North, Northeast, and East entrances. The Old Faithful area is accessible from the South and West entrances.