Spring (March to May) and autumn (September to November) are the best times to visit. Temperatures are comfortable, the light is warm and golden in the late afternoon — ideal for photographing Monument Valley's buttes — and the crowds are manageable. Wildflowers can appear on the desert floor after a wet winter.
Summer brings intense heat, regularly topping 38°C (100°F), and the monsoon season (July through September) can produce flash floods that close roads into Monument Valley without warning. The valley floor roads are unpaved and become impassable when wet.
Winter is cold, occasionally snowy, and roads can ice up. Monument Valley in a dusting of snow is spectacular if you can handle the uncertainty, and hotel rates drop sharply. Whatever season you visit, bring more water than you think you need — the high desert is unforgiving.