When to go?
Bulgaria calls itself a year-round destination, and it is true that it provides activities throughout the year. The Black Sea season lasts from May to October, with an ultra-busy period from late June to the end of August. In the winter the coastal resorts are deserted and almost all hotels are closed.
The skiing season runs from December to April, though there's often enough snow left in May to enjoy a few runs, especially in Bansko (which has the best snow record). Most package tours to the ski resorts stop just after Easter, so you'll need to travel independently to ski after that date.
Hiking can commence in the mountains almost as soon as the snows have melted, and stops as the snows arrive. It can be hot for walking in July and August, but spring and autumn are ideal seasons. The same is true for general touring or visits to the capital.
Most of Bulgaria enjoys a covering of snow in the winter, and because it sits at the boundary between two massive weather systems it can be prone to extremes of every condition. Impressive thunderstorms can happen at all times of year and rain is also a possibility whatever the season.