The climate varies widely depending on the elevation. In the southern border areas it is tropical; at the other extreme, in the high Himalayan regions, there is perpetual snow. Temperatures in the far south range from 15°C in winter (December to February) to 30°C in summer (June to August). In Paro the range is from -5°C in January to 30°C in July, with 800mm of rain. In the high mountain regions the average temperature is 0°C in winter and may reach 10°C in summer, with an average of 350mm of rain.
Rain occurs primarily during the southwest monsoon season from June to September. Bhutan bears the brunt of the monsoon, receiving more rainfall than other Himalayan regions – up to 5.5m a year. During the monsoon, heavy rain falls almost every night; in the day there may be long periods without rain. Low clouds hang on the hills, obscuring views and, if they are too low, forcing the cancellation of flights at Paro airport.
Precipitation varies significantly with the elevation. The average rainfall varies from region to region.
- Himalayan regions Less than 500mm per year.
- Inner central valleys 500mm to 1000mm per year.
- Southern foothills 2000mm to 3500mm per year.
- Southern border area 3000mm to 5000mm per year.