Incident Commander Tom Clemo told reporters the blaze was "probably the largest, most destructive fire in Washington's history," a claim state officials had not disputed as of Sunday afternoon.
The fire, named Old Trails, is one of at least a dozen burning across more than 200,000 acres of Washington, part of what officials are now calling one of the state's most destructive wildfire stretches on record.
Volunteers at the shelter have included therapy dogs from Lutheran Church Charities and a county fire chaplain offering counseling, alongside cots, food, water and pet supplies for evacuees who, in many cases, do not yet know whether they have a home to return to.
FEMA has since approved Fire Management Assistance Grants to help cover firefighting costs.
The National Weather Service's "particularly dangerous situation" designation issued Saturday, reserved for conditions a step beyond a standard red flag warning, had never been used in Washington before this weekend.
The confirmed damage from the fire that jumped the Spokane River Saturday night has climbed from an overnight estimate of 50-100 structures to a confirmed 640, as officials stop short of ruling out fatalities and thousands remain evacuated.