October through April is high season — daytime temperatures in the seventies and eighties Fahrenheit, cool nights, dry sunshine. Most major events fall in this window: the Tucson Gem and Mineral Show in late January and early February (with hundreds of satellite shows across the city), the Tucson Rodeo and Rodeo Parade in February, the Fourth Avenue Street Fair in March, the All Souls Procession on the weekend after Halloween, and the Sonoran Hot Dog Festival in March.
May, June and September can be very hot — over 100°F is normal. The summer monsoon arrives in July and August: dramatic afternoon thunderstorms, lightning shows, flash floods in the washes, the smell of creosote in the rain. It is when Tucson is most alive even though the heat is at its peak.
In the depths of winter the cool nights drop to 40°F; the high country in the Santa Catalinas occasionally gets snow, and the Mount Lemmon ski hill briefly opens.