You can expect moderate tremperatures during the day, 12-15 C, temperature dropping at night and getting colder. It can snow in Paro and Thimphu. Punakha is warmer. If you go up in the mountains, the higher the colder it gets.
Bhutan is a wonderful place to visit, and best visited in Autumn or in Spring. With both the season offers you the wonderful scenic view of voluptuous mountains and lush green valleys with beautiful flowers. Sky shrouded with clouds and a peace of mind. February will have some cold chilled mornings but if you are a winter lover you will enjoy this place in Feb too. All the best for your trip.