Southern Arizona in September

October through April is prime time—daytime highs in the 70s and 80s, perfect for hiking and exploring. January and February bring the best weather but also the biggest crowds and highest prices. March sees wildflower blooms in good rain years. Here's the thing about summer: locals flee, prices drop dramatically, but temperatures regularly hit 110°F. Pool weather starts in May and doesn't really end until October. Monsoon season (July-September) brings afternoon thunderstorms that can flood washes within minutes. Winter nights can surprise you—it actually snows on Mount Lemmon, and desert temperatures can drop into the 30s.