The Flat Fire north of Sisters near Lake Billy Chinook grew to more than 18,000 acres by Aug. 23 and widespread evacuation orders are in place.
The largest wildfire in the state broke out on Aug. 21 and grew rapidly on dry, hot and windy conditions that fueled the flames.
A red flag warning has been issued for the fire from Aug. 24 into Aug. 25, meaning that the blaze could grow over the coming two days.
Level 1, 2 and 3 evacuation orders include a widespread region between Sisters and Lake Billy Chinook. An evacuation map can be found here.
Air quality ranged from unhealthy to very unhealthy in Sisters and Bend due to smoke from the fire.
By the evening of Aug. 23, fire officials said they expected the Flat Fire to calm overnight with temperatures cooling and humidity increasing. Northernly winds that have been driving the fire also are expected to moderate.
"A dry and unstable air mass with warm temperatures can contribute to active fire behavior," the warning said.
A large team of firefighters are working the blaze on the ground and in the air. Oregon Gov. Tina Kotek declared a conflagration and the Oregon State Fire Marshal Red Team is attempting to protect homes in the potential path of the fire.
Some parts of Lake Billy Chinook are closed, so visitors should check conditions before arriving.
Zach Urness has been an outdoors reporter in Oregon for 18 years and is host of the Explore Oregon Podcast. He can be reached at [email protected] or (503) 399-6801. Find him on X at @ZachsORoutdoors and BlueSky at oregonoutdoors.bsky.social. Urness is the author of "Best Hikes with Kids: Oregon" and "Hiking Southern Oregon."