Sedona's climate is governed by its elevation — at 4,500 feet it is cooler than Phoenix by about 20°F (11°C), making it pleasant when the desert floor is unbearable. Spring (March–May) and autumn (September–November) are the most popular seasons, with daytime temperatures in the 60s–70s Fahrenheit (15–25°C) and clear skies for hiking and photography.
Summer (June–August) brings heat — daytime highs reach the 90s°F (32–35°C) — but also the Arizona monsoon, which brings dramatic afternoon thunderstorms from roughly mid-July to mid-September. The storms roll in fast and the lightning over the red rocks can be spectacular. Trails should be avoided during storms. Many visitors prefer summer mornings (cool and often empty) followed by indoor time during afternoon storms.
Winter is quiet and cold at night (below freezing is common in December and January) but often beautifully clear. Snow does fall occasionally and covers the red rock in white with surreal effect. The summer and Easter holiday crowds are entirely absent.
The crowds peak at spring break (mid-March), over Thanksgiving, and during the Sedona Film Festival in late February. If you want the trails to yourself, aim for a weekday in November or early December.