Spring and Autumn are the best time to visit Bhutan. Having said so, summer and winter have their own draws and attractions.
Spring is the favourite time to visit Bhutan. Nature lovers who are keen on local flora should consider visiting Bhutan end of April or in May. Flowers would be in full bloom then.
Fall is another high and crowded season for Bhutan. Though Bhutan does not offer browning forest nor Maples, the mild weather in autumn makes it a perfect time to visit Bhutan. Thimphu Festival usually takes places at the end of September or early October.
If you like to avoid the higher tariff and the cold of winter, consider visiting Bhutan early June. If the monsoon is late, the whole of June will be great for traveling. Monsoon will be in its earnest in July. Having said so, our personal experience with monsoon in Bhutan has been limited to afternoon light shower once every 2 to 3 days. Some outlying district such as Gangtey can be given a miss as the country road can be swollen with mud. Summer often offers vibrant green foresting and flourishing paddy fields against a backdrop of the clear blue sky after the rain.
To avoid the crowd and catch the Black-Necked Cranes, winter would be the time to go. To catch Himalayan blue sky without paying the additional tariff, consider visiting Bhutan in December. The temperature will not be too cold yet as lowest temperature usually takes places near the end of January. In January or February, Paro and Thimphu may experience a one-day snow.