Spring (March–May) is the best time to visit Moab. Temperatures are warm but manageable — daytime highs in the 60s–70s°F — the wildflowers are out in the canyon, and the light on the red rock is at its most vivid. This is also when the parks are busiest, particularly spring break weekends in March and April. Book accommodation months in advance.
Autumn (September–October) is excellent, with similar temperatures to spring and fewer crowds after Labour Day. The cottonwood trees along the Colorado River and canyon bottoms turn yellow in late October.
Summer (June–August) is brutally hot — temperatures regularly exceed 100°F, the slickrock radiates heat, and there is almost no shade on trails. The national parks are at their most crowded. If you must come in summer, do all hiking before 9am, drink enormous quantities of water, and don't attempt the Delicate Arch hike in the afternoon.
Winter (November–February) is cold but quiet. Snow occasionally covers the parks, making them extraordinarily beautiful and nearly empty. Some trails require microspikes; others are simply icy. Most tourist infrastructure stays open year-round, though a few outfitters close for winter.
The Moab Folk Festival runs in early November and draws a good crowd to town; the Easter Jeep Safari in late March/early April brings thousands of 4x4 enthusiasts and can make accommodation impossible to find.