One of the most popular reasons for visiting Bhutan is to go trekking, and if this is the purpose of your visit then the seasons and their varying weather needs to be a consideration when you are planning what time of year to visit Bhutan. The months of September and November are the best for trekking. During these months the skies are generally clearer and the mountain peaks look stunning against the clear blue skies. Although these are the best months, you should still expect to experience some rainfall. Autumn is a very popular time for all types of tourists to visit Bhutan, over half of the annual tourist numbers come during these few months. This is partially due to the weather, but also because of the popular Thimhu tsechu (dance festival) as well as the return of the black-necked crane to the country.
Outside of the peak autumn months, winter is a good time for bird watching but gets very cold at night, spring also offers good but wet trekking and the spring flowers are beautiful, and summer is monsoon season when 500mm of rainfall falls in three months, but the dark clouds contrast against the green rice paddies offering fantastic photographic opportunities.