Winters in Rishikesh mean clean, crisp and cool air with pleasant temperature. The low is about 6 degrees Celsius. Winters would be the best time to visit Rishikesh.
During the summers the temperature goes as high as 40 degrees Celsius and lows are about 15 degrees Celsius. The heat is sometime bad and the weather is not conducive for sightseeing.
Monsoons bring heavy rainfalls and humidity in the region. So unless you don’t mind the showers, you can plan a trip to Rishikesh during these months. Do not forget to pack your umbrella.