Due to the undulating terrain of the state, temperature can vary widely throughout due to the altitude. Generally, the towns at lower altitude, Singtam, Rangpo, Jorethang etc, will be warmer while those at the higher altitudes (Gangtok, Namchi, Mangan) can be cold to visitors who are used to tropical climate.
The hilly terrain of Sikkim starts in the south at the border with the neighbouring state of West Bengal. As one continues along the national highway and entering Sikkim through Melli, the altitude starts to rise gently as one drives towards Gangtok (1,650m/5,410 ft), Yumthang (3,564m/11,693 ft), Ravangla (2,134m, 7000 ft) and Pelling (2,150m/7,200 ft).
Sikkim experiences the four seasons - Spring, Summer, Autumn and Winter with heavy rain during Summer and Winter.