October and November are the best months. The southwest monsoon has retreated, the air is fresh and green, and temperatures are comfortable (typically 20–28°C). October brings Dasara, the ten-day festival that culminates on Vijayadashami — the palace is illuminated every evening, a grand procession of decorated elephants carries the palace idol through the city streets, and the entire city turns out. Dasara is one of India's grandest public festivals and timing a visit around it is worthwhile, but book accommodation months in advance.
December through February is cooler and dry — pleasant for sightseeing though the nights can be surprisingly cold. March to May brings the pre-monsoon heat, with temperatures peaking above 35°C. The monsoon (June to September) brings rain and lush greenery; the Brindavan Gardens look their best, the waterfalls above Ooty run full, and Mysore itself is manageable — it sits in a rain shadow and receives far less rain than the coast or the Nilgiris.