By midday Saturday, Aug. 2 -- leave now. The Old Trails Fire had moved fast enough overnight that Spokane County authorities elevated the evacuation status for communities northwest of the city to Level 3, the most urgent designation, meaning there is no time to wait.

twelve large fires were burning across Washington, consuming more than 312 square miles of land, and the conditions driving them showed no sign of easing.

The heat dome has been building for days, spreading from the Pacific Northwest south through the desert Southwest in a pattern forecasters described as unusual not for its existence but for its intensity at this time of year. Las Vegas registered 115 degrees Fahrenheit on Saturday, within reach of its August record of 11...