Due to the extreme altitude, there is an immense variation in climate and vegetation. With a rainfall of about 140 inches in Gangtok, the climate is
tropical up to 5,000ft, temperate between 5,000ft–13,000ft, alpine at 13,000ft, and snowbound at 16,000ft and above.
The best time to visit Sikkim is between mid-March and June but especially, April and May, when the rhododendrons and orchids are in bloom. However,
temperatures can be high, especially in the valleys. During the monsoons, from the end of June until end September, rivers and roads become
impenetrable, though plants nurtured by the incessant rain erupt again into bloom towards the end of August. October, when orchids bloom once again and
November tend to have the clearest weather of all. As December approaches, it gets bitterly cold at high altitudes, and remains that way until early
March, despite long periods of clear weather.
The best time to visit this zone is from mid September to mid December, although it gets pretty cold by December. The high seasons again starts from
mid-march & continues till mid June. During monsoon months ie; from June to September, the view of the mountains gets obscured & rainfall is pretty
heavy (270 cm annually).