As suggested by Sikkim Tourism, the best time to visit Sikkim is either between March and May or October and mid-December.Winter (December to February) is extreme in Gangtok and it can be very cold out there particularly early in the mornings and at nights. The average temperature hovers around 4°C.
Sikkim also has five seasons but the best time to visit Sikkim is autumn between Octobers to November. If you love to watch Sikkim snowfalls season, then you must visit in the winter season.The best season to visit Sikkim is during the months of September to October and from February to April i.e before the monsoon sets in.
IN March to June the weather remains pleasant. The skies are clear blue, giving maximum visibility to see distant mountain ranges. The nights can still be cold, but the chill is enjoyable. The summer months are peak season for tourists as many families visit during this time, due to children having summer vacations. For adventure lovers, summer is a good time for trekking in Sikkim.