The climate in Bhutan typically varies; tropical in southern plains; cool winters and hot summers in central valleys; severe winters and cool summers in North. The terrain: mostly mountainous with some fertile valleys and savanna. For Thimphu in January the daily average maximum temperatures is 1°C with the average minimum -17°C, while in June the average maximum is 12°C with a minimum of 3°C. The wettest month for Thimphu is August with an average of 106.2mm of precipitation falling while the driest month is December with 2.2mm falling.
The following charts show yearly weather trends with information on monthly weather averages and extremes.
Temperature
The chart below plots the average high and low temperature for each month of the year. It also shows the maximum and minimum recorded temperatures.
Precipitation Amount
The chart below plots the average monthly precipitation amount.
Rain days
The chart below plots the average number of days in any month that you can expect to see rain falling.
Snow days
The chart below plots the average number of days in any month that you can expect to see snow falling.
Wind Speed
The chart below plots the average daily wind speed you can expect for any month. It also shows the maximum recorded sustained wind speed for each month.
source: http://www.myweather2.com/Holiday-Destinations/Bhutan/Thimphu/climate-profile.aspx