December is the start of winter in Bhutan. Temperatures aren't quite as cold as in January, but there's not much difference, especially later in the month.
The altitude plays a large role in just how cold places in Bhutan get in winter, though. While most of the country is at a high altitude, not all of it is. Southern parts of the country border India, so the climate around the wildlife-filled Royal Manas National Park is much more like a North Indian climate. The town of Gelephu ranges from 52 to 77° F (11 to 25° C) on average in December.
At the other end of the spectrum, many points of interest to travelers are at a higher altitude. Punakha is at around 5000 feet (1500 meters) and experiences December temperatures between 43 and 68° F (5 and 17° C). The capital Thimphu is higher and therefore colder, at around 6500 feet (2000 meters), and sees temperatures between 30 and 59° F (-1 and 15° C).
The upside to weather in December, and the whole winter, is that skies are normally clear, allowing good mountain views.
Crowds & Costs
The winter months are low season in Bhutan, and not many travelers visit in December. You'll pay low-season prices for tours and lodging, and may even be able to find a great deal on some of Bhutan's beautiful boutique and luxury accommodation.
Where to Go
It's preferable to stick to Western Bhutan in December and the rest of the winter, as roads to the east are closed due to snow on the high passes.
If you're interested in jungle national parks and wildlife tours, winter is ideal, as this is a perfect time to visit the low-altitude Royal Manas National Park. It's just 200 to 360 feet above sea level, so much lower than most places of interest to visitors in Bhutan. You can see tigers, rhinos, elephants, and leopards. As mentioned above, December temperatures can actually be quite warm.
What to Do
Trekking at higher altitudes is not usually possible in mid-winter, but some shorter hikes and walks are still possible. With clear skies and mountain views, winter is a good time to get out into nature, as long as you avoid very high-altitude routes or camping. The Punakha Winter Trek, for example, passes through villages, forest, and farmland, and doesn't go too high in altitude.
General touring is also a good idea in December. You'll go out in the daytime to see Bhutan's famous temples, palaces, and monasteries—like the Tiger's Nest Monastery and Punakha Dzong—and return to warm and cozy accommodation in the evening. Whatever kind of accommodation you're staying at, don't pass up the opportunity to try a traditional hot stone bath. These are usually available for a small fee.
Events in December
Trashigang Tsechu, early December. Trashigang's festival is one of the largest in eastern Bhutan. While eastern Bhutan can be difficult to reach in December because of snow blocking the passes, you may be able to reach there via air, or overland as this festival is early in the month.
Druk Wangyel Tsechu, Thimphu, mid-December. This festival is unusual in that it's not monks or laypeople who perform the dances, but members of the Royal Bhutan Army.
National Day, 17th December, commemorates the coronation of the first King of Bhutan in 1907.
Traveling to Bhutan in December? Check out these great itineraries
Bhutan Highlights: Thimphu, Punakha, and Paro - 6 Days. This itinerary lets you see the highlights without venturing into the colder higher altitudes.
Bhutan Highlights - 7 Days. Visit the iconic Tiger's Nest Monastery, admire the beauty of the Paro Valley, and learn about Bhutanese culture on a week-long trip.