Firefighters already faced extreme fire behavior, with dry fuels and high temperatures, and were on watch for gusty winds and the threat of lightning strikes from thunderstorms expected through Thursday.
The Kittitas County Sheriff's Office ordered residents of about 75 scattered homes and cabins to evacuate, and several recreation areas were closed.
The fast-moving Colockum Tarps Fire, which originated south of Wenatchee, burned to the north end of the Wild Horse Wind Farm, about 17 miles east of Ellensburg overlooking the Columbia River.
Firefighters made progress on stopping the fire's spread, except in the southwest corner, fire spokesman Peter Frenzen said. In addition, thick smoke prevented air tankers and helicopters from dropping retardant and water on critical areas of extreme fire growth.
At least 370 firefighters were working to control the blaze, which was 8 percent contained, he said.
Due to the fire's growth, Frenzen said fire managers also would establish a satellite fire camp in Kittitas County for firefighters to eat and rest each evening, to allow them to avoid driving to the main fire camp south of Wenatchee.
Near Goldendale, firefighters gained ground on a blaze that had closed U.S. Highway 97 for days.
The Mile Marker 28 Fire was 60 percent contained. The Washington Department of Transportation reopened the highway Wednesday, with pilot cars leading vehicles through the fire area. Delays of up to one hour were expected.
Crews built a fire line around the flames that charred about 40 square miles near Satus Pass, about 15 miles northeast of Goldendale, fire spokesman Dam Omdal said.
More than 1,300 firefighters were mopping up hot spots and strengthening fire lines.
The cause of both fires remained under investigation.