The fires have destroyed at least 600 buildings near the state's second-largest city, Spokane.
About 100,000 hectares have burned in Washington, and several of the wildfires are still burning out of control.
The weather is expected to remain dry in the coming days and, according to Senator Maria Cantwell, it will be "challenging" for firefighting authorities.
Fires are also ongoing in the neighboring states of Idaho and Oregon, threatening agriculture.
