The southern part of Bhutan is tropical, and in general, the east of Bhutan is warmer than the west of the country. The central valley of Punakha, Wangdiphodrang, Mongar, Trashigang and Lhuntse enjoy a semi tropical climate with very cool winters, while Thimphu, Trongsa and Bumthang have a much harsher climate, with heavy monsoon rains in the summer and heavy snow fall in winter. Winter in Bhutan starts from mid-November till mid-March, and at this time of the year the climate is dry with day time temperature of 16-18° C and night time temperature falling below zero. The monsoon usually arrives in mid-June, with the rain falling mainly in the afternoons and evenings. Autumn starts from the end of September, after the last of the big rains, and it is a magnificent season for trekking-lasting till mid-November.
Annual Average Temperatures of different places are as follows:
The temperature listed above are all in degree centigrade.