Kathmandu in September

October through December brings clear mountain views and perfect trekking weather. Temperatures hover around 20°C during the day, dropping to 5°C at night. March through May works too, though it gets dusty and hazy before monsoon season hits. Avoid June through September — the rain turns streets into rivers and mountain views disappear behind clouds. Winter months (January-February) can be surprisingly cold, especially at night, but you'll have temples mostly to yourself. Book accommodations ahead during October peak season, or you might end up sleeping on someone's rooftop.