Sikkim’s geographical location with its altitudinal variation allows it to have sub-tropical temperature conditions in the southern lower parts to tropical, temperate, alpine and cold desert climatic conditions in the snowy north within this small area of 7,096 kms. Temperature varies with the altitude and the slope. In lower altitudes, the temperature is between 4.5 °C to 18.5 °C, whereas at higher altitude, it varies from 1.5 °C to 9.5 °C. Still higher up, the temperature can go below -30°C. The average annual rainfall is 2739 mm. Rainfall varies widely between sheltered valleys, foothills and high mountains and is heavy and well distributed from May to early October. July is usually the wettest month. The highest annual rainfall for the individual station may exceed 5000 mm. and average number of rainy days (days with rain of 2.5 mm. or more) ranges from 100 at Thangu in North Sikkim to 184 at Gangtok in East Sikkim. The state experiences frequent landslides, an aftermath of the torrential downpours during monsoon. Fog is another common feature from May to September. During winter, temperature rarely rises above 15°C.and snowfall occurs during the winter months in the higher elevations.