The warning, effective until 7:15 p.m. MDT, covers Ada, western Elmore, Canyon and northwestern Owyhee counties.

Extreme heat warnings remain in place for parts of southeast California, southern Nevada and much of Arizona -- where high temperatures between 108 and 118 degrees are possible through Friday. Record high temperatures are also possible for Phoenix and Tucson, Arizona, through Thursday, as well as Albuquerque through Friday.

As Canada grapples with one of its worst wildfire seasons on record, smoke from the blazes have prompted air quality alerts across the U.S.