Bhutan has a season for everyone. 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 centre and up to the alpine world of tower of Himalayas and glaciers of the east.
Spring and Autumn are definitely the best time to visit Bhutan. Having said so, summer and winter have their own draws and attractions
In Winter dry and pleasant conditions make this the best time of the year for bird watching in the jungles, village to village trekking in the lower altitudes or a bicycle trip along quite mountain roads. The trekking routes in the high mountains are covered in deep snow and are impassable at this time of the year. The impressive and endangered Black Necked Cranes spend the winter in the high valley of Bumdeling (Trashiyantse, in the Eastern Bhutan and Phojikha (Wangduephodrang, in the Central Bhutan).
In Spring the trekking season commences in moderate altitudes. Above 3000 metres spectacular rhododendron forests bloom. In Paro, one of the largest monastic festivals, Paro Tsechu, takes place. The temperature is plesantly mild even up to the Alpine regions. Rain comes only in May as the harbinger of the approaching monsoon.
The Summer brings with it the monsoon, but this should not deter travelers. In the settled areas 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. Treks in high mountain areas, e.g. the Snowman Trek, are characterized by mild temperatures, verdant green meadows, and pastures of Blue Poppies and Edelweiss. Nomads tending their yaks in the high mountains are common sight.
And lastly, Autumn is the traditional High season in Bhutan. September and October have the highest number of tsechues(Monastic festivals). Trekkers particularity enjoy the clear view of the mountains in October and the low rain-fall. Rice harvest means a picturesque landscape, remarkable terraces and changing color.
Temperatures and vegetation in the altitudes between 200 and 300 metres are comparable to the moderate climate of middle Europe. The tree line lies just under 4000 metres. During winter there is little precipitation. Snow falls rarely below 2500 metres.