From tourist perspective, most of the places of interest are located in mid -west, mid central and east. And due to some of its topographical and climatic features enjoys pleasant weather through out the year unlike upper northern region with extreme cold in winter and south with hot, humid and wet summer.
Altitude influence the climate
Mountains, hills governs the landscape of Bhutan, although Bhutan lies at par in latitude with Jaipur and Agra in India, however it experience dramatically different weather condition than these places, owing reason to the altitude, as most places of interest are located above 1300 to 3100 m above the sea level.
Topography, Vegetation and Weather
The topography of Bhutan can be aptly compared to mammoth and steep staircase, rising from 150 meters from sea level to the snowy peak of above 7000 meters. Within the distance of 240 kms, there is kaleidoscope of semi tropical to temperate to freezing alpine climatic conditions.
It can be categorically divided into three geographic zone.
1.The foothills of south
2. The central temperate zone.
3. Above the temperate zone ( Sub alpine or alpine zone)
The foothills of south
It rises from plains to an altitude of 1500 m and have thick evergreen forests, fertile farmland and relatively high populations. The border town like Phuentsholing, Gelephu and Samdrup Jonkhar are enclosed under this zones. The climate is generally hot, humid in summer and pleasant winter.
These places serves as port of entry and exit for guests travelling over land. However, other than the above places, most of these foothills region fall under restricted zone in term of tourism.
The average temperature in summer 30 C and winter 19 C
The central temperate zone.
This zone encompasses the most places of interest like Thimphu, Paro , Haa, Punakha, Bumthang Trongsa etc. It cut off from foothills by the high ranges of Inner Himalayas and has succession of valley at altitude varying from 1500 to 3500 meters. The vegetation mainly consist of conifers, oak, magnolia, maple, birch, rhododendron, willow, poplar etc. When the plains of india blazes with heat wave and plagued with humidity and stickiness, the summer in Bhutan remains cool and pleasant and the winter are cold during night but relatively warm with bright sunshine during day. This zone also harbour some of short yet popular and beautiful trek like Druk Path, Haa -Juniper, Haa-Bumdra and in low altitude region of Punakha and Trongsa, the trek like Samtegang & Nabji Korphu respectively flourishes during winter.
The average temperature during can go to approx. 22 C in summer and in winter it can be around 12 C especially in Thimphu & Paro, and in Punakha/Wangdi 28 C in summer and 19 C in winter as it lies in lower altitude than Thimphu/Paro.
Above the Temperate Zone
This zone fall at altitude ranging from 3500 meters to 5500 meters. are the subalpine and alpine highlands, ringed by the towering snow clad peaks of the greater Himalayas, Mt Chomolari (7300 m) and our highest peak Mt Gangkar Phuensum (7541 m). The winter is harsh, freezing and passes remains blocked with snow and throw only small window of accessibility during spring and autumn season. And during this period, the trek like Chomolari and challenging Snowman Trek comes into play. This zone boast beautiful glacial lakes and pastures covered with wild flower like dwarf rhododendron, edelweiss, fritillaries, primulsa and national flower blue poppy.
The average temperature during spring is 10 C and in autumn it is 8 c
Best time to visit
Plainly speaking, its good to travel throughout the year. Many consider spring and autumn as best season for the reason not only of weather but also some of prominent festival in western Bhutan fall during this period. In all likelihood, integrating good weather with festivities can be good, however the shortcoming likely, it can be crowded and infrastructure like hotels, good guide, and transport can be stretched.
Even the season like monsoon (June, July, Aug) and winter (Dec, Jan, Feb), other than spring (March, April, May) and autumn (Sept, Oct, Nov) that complete the cycle of weather in a year, are generally depicted in poor light and underrated online. Monsoon in central temperate region or underlying region of places of interest are in form of light shower as it fall under rain shadow. The moisture laden southeast monsoon shed its rain in foothills of south thus its wet in southern Bhutan. By the time it reaches the central temperate regions its in form of drizzle or light shower, which in-fact add a freshness to the environment.
Winter in central temperate region are generally warm filled with bright sunshine offering clear vista of far off mountains peaks during day time in winter. During night it can be cold but during that time you will be basking in warmth of room heater. Succession of valleys which houses attractions are segregated by high passes and its likely to have snow in these passes during winter like Docula, Chelala etc. Barring a few exception in the past, the weather in valley remains great even during winter.