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 – February) to 30°C in summer (June – August). In Paro, the range is from minus 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.

Only in the high Himalayan regions does the snow remain year round – in the form of glaciers. Some snow falls in northern and central Bhutan but does not remain on the ground for long. As a general rule, snow melts immediately below 2400m, stays a short while (longer in shaded areas) between 2400m and 3500m, and remains on the ground until early March above 3500m.

Rain occurs primarily during the south-west 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 and during in the day, there may be long periods without rain. Very little rain falls during the autumn from October to December, making this the ideal season for trekking and mountain viewing.