Bhutan is a spectacular destination year-round, although the weather varies dramatically depending on the elevation and season. The best time to visit Bhutan really depends on what you're looking for.
Here's a look at Bhutan's seasons:
From March to May, Bhutan's abundant flora is on full display and the weather is fantastic, mild with occasional mountain views. Though there is some rainfall, particularly as you get into May, temperatures top out around 70 degrees Fahrenheit. Rhododendron forests fill with color and if you're lucky you may even spot the rare blue poppy, a three-foot tall species once thought only to be a myth. The Punakha and Paro festivals draw many travelers at this time of year.
The long days of summer in Bhutan tend to be uncrowded, verdant, and less rainy than most visitors expect. Afternoon showers generally occur each day during the green season, with July and August receiving as much as 14 inches per month. However, the heavy rains often fall during the night, so while low clouds may hang on the hills and sometimes obscure views by day, it is also common to experience long periods without rain. If you want to escape the crowds, capture some great deals, see the country at its most lush green or enjoy the uniquely intimate Gangtey festival, this is the time to travel to Bhutan. It's also a nice season to spend time at a spa or in a meditation room if you opt to stay at Bhutan's more luxurious hotels.
Fall in Bhutan boasts the largest festivals, pleasant temperatures, and world-class mountain vistas. From September to November, some of the largest Bhutanese festivals, including the Thimphu tshechu, take place. This time of year the weather tends to be idyllic, with highs in the 70s and little rain. Later in the season, the sky becomes clearer, revealing vivid mountain views. On a clear day at the top of the Dochu La (10,000-foot pass), 200 miles of Himalayan summits are stacked before you.
From December to February, you'll find a pristine, private wonderland with the clearest skies of the year. Winter in the Himalaya can certainly be cold, especially at higher elevations. However, Bhutan is at about the same latitude as Florida and not as cold as many travelers expect. In the lower valleys, such as Punakha, temperatures can reach the 50s and even 60s. A winter visit to Bhutan means small crowds, spectacularly clear views of the Himalayan range, and a chance to see the endangered black-necked cranes.