Considering its small area Bulgaria has an unusually variable and complex climate. The country lies between the strongly contrasting continental and Mediterranean climatic zones.
The country's half-dozen mountain groups play a significant part in determining regional variances. The Balkan Mountains are the southern boundary of the area in which continental air masses circulate freely. The Rhodope Mountains mark the northern limits of domination by Mediterranean weather systems. The area in between, which includes the Thracian Plain, is influenced by a combination of the two systems, with the continental predominating.
Although located at the same latitude as southern New England, Bulgaria's climate is noticeably more temperate.
Although the climate is generally temperate and pleasant, its variability throughout the year means that it may at times be uncomfortably cold in winter and rather warm and sultry in summer.
Winters are cold but not bitterly so. In the south and Black Sea coastal regions, Mediterranean influences temper the harsher continental climate of the interior.
Spring can be a very changeable season with rapid alternations between warm and cold days. Daily hours of sunshine range from about two in January to as much as ten in midsummer.
Summers are typically hot and dry, but rarely oppressive, with moderate relative humidity. Dry summers and mild, humid winters prevails in the valley of the southwestern Rhodope Mountains. The Balkan Mountains are the northern limit of this climatic zone.
Autumns are mild and pleasant in Bulgaria. The multi-coloured forests in autumn add to the picturesque landscape. Autumn showers in principle are more frequent than in spring.
The wettest period is early summer throughout most of the country, except in the southern valleys, where most precipitation falls in autumn or winter.
May, October and November are the rainiest months.
The average rainfall is about 635 millimetres (25 inches) per year, ranging from a low of 193 millimetres (8 inches) in the northeast to a high of 1,905 millimetres (75 inches) in the Rila Mountains.
The average annual temperature is about 13°C (55°F).