Boise, Idaho – Southwest Idaho will bake under near triple-digit heat on Saturday, with Boise expected to reach 99° and Fairfield hitting 100°, before a dramatic cooldown arrives Sunday.
According to the National Weather Service in Boise, a heat advisory remains in effect through Saturday evening, with temperatures peaking across the Treasure Valley and central mountain valleys. Boise, Caldwell, and Nampa will all flirt with or exceed 98°, while high-elevation spots like McCall and Stanley stay in the 70s.
The hottest stretch will peak midday Saturday, prompting officials to urge residents to drink water, limit outdoor activities, and wear sunscreen and light clothing. Cities like Mountain Home and Ontario will also reach the upper 90s, pushing heat indexes even higher in urban areas.
By Sunday, cooler air moves in rapidly. Boise drops to 83°, then settles into the upper 70s through midweek. Highs in Twin Falls, Jerome, and Idaho City follow a similar pattern, falling by 10–20° between Saturday and Monday.
This roller coaster pattern may continue through early June, with more updates expected as temperatures shift. Heat advisories remain active through Saturday evening.
