Climate in Bhutan varies drastically from place to place within a short range. The land rises from the southern moist sub-tropical foothills at an altitude of about 200 meters above sea level to snow-capped peaks of over 8,000 meters in the north. The central temperate belt, which is the touristy valleys, ranges from about 900, to 4,500 meters above sea level. The capital city Thimphu, is situated at 2,400 meters above sea level.
The climate along this belt defies generalization but it can be safely said that spring (March to May) brings warm days and cool nights with the mercury averaging 15-20 oC at daytime. With June come occasional downpours and summer temperatures peak at over 20o C. The milder months of Autumn (September to November) are less wet and are the best time of the year for trekking. But in the trekking routes during Autumn, the temperature dips below 0o C at night.
The winter months of December, January and February are the coldest and night time temperatures often plummet below – 10C in higher altitude valleys. Once or twice there are snow fall in colder valleys of Thimphu, Paro, Trongsa, and Bumthang.
Given that there are no insulation and central heating in most homes and hotels, it can be cold in winter. You will even have to wear your jackets inside rooms in winter.
However, winter offers its own charm of crystal clear sunny blue skies and unhindered view of snow-capped mountains.