October to March is the peak season for the Chepe railway journey, when the Sierra Madre climate is at its most comfortable and the canyon landscapes are at their clearest. October and November are ideal: the summer rains have ended, the vegetation is green from the wet season, and temperatures in the upper canyon are mild. December and January bring cold nights at altitude on the Chihuahua end of the route.
Los Mochis itself has a hot, semi-arid climate with most rain falling July–September. Summer is oppressively hot in the city (regularly above 38°C), which is another reason most visitors time their visit to coincide with the October–March Chepe season. The city is functional year-round as a transit point.