Bhutan has a favorable or best season for the tourists throughout the year but most tends to defer the plans during the monsoon season i.e. June-August months when the weather is sometimes a little too wet for sightseeing tours. The best time for trekking is in spring and autumn seasons i.e. March-May and September-November months. The kingdom stretches across all climatic zones from the sub-tropical jungles in the south, to the moderate heights of 2000-2500 metres in the central valleys and up to the alpine world of the towering Himalayas and glaciers of the north.
In winter season, the dry and pleasant conditions make it the best time of year for bird watching in the jungles, village to village trekking in the lower altitudes or a bicycle trip along quiet mountain roads. The trekking routes in the high mountains are covered in deep snow and are impossible during winter season. The endangered black-necked crane (Grus Nigricollis) spends the winter in the high valleys of Bumdeling in Trashiyangtse and Phobjikha in Wangdue.
In spring, the trekking season commences in moderate altitudes. Above 3000 metres valleys, spectacular rhododendron forests bloom. It is also the perfect time for a rafting tour. In Paro valley, one of the largest monastic festivals (tshechus) takes place at Rinpung Dzong in spring. The temperature is pleasantly mild even up to the Alpine regions. Rain comes only in May as the harbinger of the approaching monsoon. (Average temperatures table shown below).
The summer brings with it the monsoon, but this should not deter travellers. In the settled areas of the medium ranges of Central and Western Bhutan pleasant summer temperatures without heat or humidity can be found. Rain falls for short periods daily but is manageable with adequate planning and equipment. Mild temperatures, verdant green meadows, and pastures of Blue Poppies and Edelweiss characterize the treks in high mountain areas. Nomads tending their yaks in the high mountains are a common sight.
Autumn is the traditional high season in Bhutan. September and October have the highest number of tshechus. The trekkers particularly enjoy the clear view of the mountains in October and the low rainfall. Rice harvest means a picturesque landscape remarkable terraces and changing colour. The tree line lies just under 4000 metres. During winter there is little precipitation. Snow falls rarely below 2500 metres.