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, Wangduephodrang, Mongar, Trashigang and Lhuntshi enjoys a semi tropical climate with very cool winters, while Thimphu, Tongsa and Bumthang have a temperate climate with monsoon rains in the summer (22- 28-degree Celsius approx.) with snow-fall in winter. Winter (below 0 – 8 Degree Celsius approx.) The best time to visit Bhutan is from mid-November until mid-March, at this time of year the climate is dry, with daytime temperature of 16-19 degrees centigrade and normally sunshine and clear skies, nighttime temperatures can fall tol below zero. The monsoon usually arrives in mid-June, with the rain falling mainly in the afternoons and evenings. At the end of September, after the last of the heavy rains, autumn (warm days but nights are chilly; 17-27 D. Celsius approx.)and a magnificent season for trekking unfolds lasting until mid-November. Generally spring is warm (20 – 25 Degrees Celsius approx.).
Best season: March, April, May, September, October and November.
Monsoon: ....June, July and August.
Winter: .........December, January and February.