Central Bhutan is cool and dry during December through March, proving a good time to visit for anyone other than the most devoted sun-seekers. Temperatures in Thimphu, the capital, are an average high of about 15 °C at this time, but lows are generally not much above zero, so travelers will need to pack some winter clothing. The capital is the world's third highest, and altitude varies significantly across this Himalayan region -- the higher you go the colder it gets. The clement weather of winter and early spring make it ideal for seeking out central Bhutan's exceptional biodiversity and wildlife be it the rare golden langur primates at the foothills of the Black Mountains or the endangered and rarely-seen Bengal Tiger.
Northern Bhutan November through February is invariably bitterly cold, the Himalayas on the border with Tibet perennially covered in snow. The temperature during these winter months very much depends on elevation, but can easily plunge as low minus -20 °C and highs averaging just 5 °C. Many of the main hiking routes often have too much snow to make trekking viable at this time of year, though there may be some at slightly more manageable routes at lower altitudes.
The climate in southern Bhutan is hot and humid ranging from 15 to 35 degree Celsius throughout the year. Virtually any time of the years is good to visit. Bhutan’s southern circuit, including the districts of Samtse, Chuka, Dagana, Tsitang, Sarpang, Zhemgang and Pemagatshe form something of an ecological hub and the rich biodiversity make the region an ecological hub, ideal for trekking in tropical forests.