Sikkim's climate is sub tropical in the lower valleys, but changing fast to temperate and alpine with increase in elevation. For most of the year, it is cold and humid as rainfall occurs right through the year. The area experiences heavy rainfall due to its proximity to the Bay of Bengal. The rainfall in the north district is comparatively less than the other districts. The general trend of decrease in temperature with increase in altitude holds good everywhere. Pre-monsoon rain occurs in April-May and the south-west monsoon operates normally from the month of May and continues up to early October.
Places with a moderate altitude (4000ft to 10,000 ft) have a more or less pleasant climate from March to June and September to November. Needless to say, the winter months of December-February are very cold. Some of the better known places situated at a moderate altitude are Gangtok, Pelling, Yuksom & Lachung.
Snowfall
In the higher altitudes of 10,000 ft plus, the temperature rarely rises above 15 degree centigrade. Some of those places are Yakshey Lodge above Lachung ; Yumthang valley, Tsango Lake and Dzongri where heavy snowfall occurs during the winter months. Tsango and Yakshey sometimes receive snowfall even during April or mid-November.
Temperature
The mean temperature in the lower altitudinal zone varies from 1.5 to 9.5 degree centigrade. Temperature varies with altitude and slope. The maximum temperature is recorded usually during July and August, and minimum during December and January.
Fog is a common feature in the entire state from May to September. 
