The window from October to March is the obvious time to visit Chandigarh. Days are warm and dry, evenings cool, and the city's many gardens are at their best. February and March bring the rose bloom and the annual Rose Festival.
April and May are unpleasantly hot, with temperatures regularly above 40°C. The monsoon from late June to September is shorter and lighter than further south but can still flood the underpasses. The post-monsoon weather in September is fresh and green but bursts of heavy rain are still possible.
December and January are cold by Indian standards — overnight lows near freezing and mornings often foggy. Pack a sweater if visiting in those months.