The fires in and around Spokane, the state's second largest city, burned about 20sq/km but they were among dozens across the Western US that stretched the ability of federal, state and local agencies to fight them.
A a total of about 1000sq/km have burned across the state, and some of the fires, including those in the Spokane area, have not been contained.
The evacuees in Spokane included patients at its US Veterans Affairs hospital.
Video from the Spokane area showed buildings on fire, black smoke billowing up near neighbourhoods, and the smoking ruins of homes, with only chimneys still standing.
Several officials expressed concern that the area does not appear likely to get a break in coming days from the weather, which is expected to remain dry.
"We are not out of danger," US Senator Maria Cantwell said during a news conference with federal, state and local officials in Spokane on Sunday.
"The next couple of days will be challenging."
In western Idaho and eastern Oregon, crews using bulldozers and helicopters continued for the 10th day to fight a fire that has burned about 1360 sq/km of grassland in western Idaho and eastern Oregon.
The area is home to cattle ranches, and authorities said the fire is threatening more than 600 homes and 800 other structures.
The weather in the area was expected to remain sunny and dry well into the week, with temperatures rising to more than 32C on Wednesday. Officials say the fire was caused by lightning.
The National Weather Service issued warnings about the air quality in eastern Washington, eastern Oregon, western and central Idaho and western Montana. It issued red flag fire warnings for parts of Utah and Montana and western Nebraska, and extreme heat warnings for the southern parts of Arizona, California and Nevada and northern Montana.
While temperatures Sunday in Spokane were forecast to remain below 27C, wind gusts from 56km/h-to-72km/h had been expected by the afternoon, said Benjamin Cossel, public information officer for the federal response team from California called in to deal with the emergency.
"We have weather working against us, and we have terrain working against us," Cossel said.
Washington Governor Bob Ferguson declared a state of emergency Saturday, and the National Weather Service issued a "particularly dangerous situation" red flag alert for eastern Washington.
Heather Rosenstrater, president and CEO of Avista Corp, the area's electric and natural gas utility, said about 10,000 people were without power, down from a peak of 30,000.
"The whole northwest is heavily impacted right now," said Keila Vizcarra, the spokesperson for the federal team from California handling what's been named the Big Grass Fire in western Idaho and eastern Oregon.
11°C