The Sonora River valley has a desert climate tempered by elevation — Banamichi sits at around 600 metres, which keeps temperatures more bearable than the lowland desert to the west.
October to April is the most comfortable window. Daytime temperatures in winter run from the mid-teens to low twenties (Celsius), with cool nights that can drop near freezing. This is peak season for the Ruta Rio Sonora, and the time when the valley's orange groves and pomegranate orchards are at their best.
May and June are hot and dry — daytime temperatures regularly reach 38–40°C, and the landscape bakes. Unless you are heat-adapted or have no choice, this is not the time to visit.
July to September brings the monsoon season, when afternoon thunderstorms roll in from the south. The hills turn briefly green, the river runs with more purpose, and the temperatures ease slightly. Flash floods are a real hazard on the dirt roads into the backcountry; pay attention to conditions before heading out to the hot springs.
Day of the Dead (early November) and the feast day of Nuestra Señora de Loreto (December 10) bring the most life to the plaza. If your timing allows, either is worth catching.