Spring (March to May) and autumn (September to November) are the best times to visit Kingman. Temperatures are comfortable — typically in the 60s and 70s Fahrenheit — and the desert is at its most appealing.
Summer is brutal. Kingman sits at 3,300 feet, which takes the edge off Phoenix-level heat, but July and August regularly hit 100°F or more and hiking in the valleys is unpleasant. The Hualapai Mountains stay cooler and offer a useful escape, but the desert drive to Oatman should be done early in the morning.
Winter brings genuine cold to Kingman. Frost is common from November through February, and snow occasionally falls downtown, with heavier accumulation in the Hualapai Mountains. The mild winter days can be pleasant for sightseeing, and there's far less traffic on Route 66 than in peak season.