Gangtok has decent weather throughout the year and temperatures rarely soar above 22 degrees Celsius.
There are 5 seasons each with their own unique appeal so you can visit almost throughout the year:
Spring and Summer: March to May is a lovely time to visit. The flowers are in full bloom and there is a lot to see and do in the place. The month of April is the best time because the tulip Garden is open to visitors and it is a rare and wonderful experience to be felt.
Monsoon: Monsoon sees a lot of Fog but the billowy fog often bathes the place in tremendous beauty. This period lasts from June to September.
Autumn: October and November see clear skies and a beautiful view of the mountains and hence are a very popular time to visit as well.
Winter: Winter is also engulfed in Fog but a great time to visit since the lakes look even prettier when they are frozen. However, it is most likely that the road to Nathula will be closed during this time.