Geography of Bulgaria - Climate

Climate

Considering its small area, Bulgaria has an unusually variable and complex climate. The country lies between the strongly contrasting continental and Mediterranean climatic zones. Bulgarian mountains and valleys act as barriers or channels for air masses, causing sharp contrasts in weather over relatively short distances. The continental zone is predominant, because continental air masses flow easily into the unobstructed Danubian Plain. The continental influence, stronger during the winter, produces abundant snowfalls; the Mediterranean influence increases during the second half of summer and produces hot and dry weather. The barrier effect of the Balkan Mountains is felt throughout the country: on the average, northern Bulgaria is about one degree cooler and receives about 192 millimetres (7.6 in) more rain than lowlands of southern Bulgaria. Because the Black Sea is too small to be a primary influence over much of the country's weather, it only affects the immediate area along its coastline.

The Balkan Mountains are the northern 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 between, which includes the Northern Thracian Plain, is influenced by a combination of the two systems, with the continental predominating. This combination produces a plains climate resembling that of the Corn Belt in the United States, with long summers and high humidity. The climate in this region is generally more severe than that of other parts of Europe in the same latitude. Because it is a transitional area, average temperatures and precipitation are erratic and may vary widely from year to year.

Average precipitation in Bulgaria is about 630 millimetres (24.8 in) per year. Dobrudja in the northeast, the Black Sea coastal area, and small part of the Northern Thracian Plain usually receive less than 500 millimetres. The remainder of the Northern Thracian Plain and the Danubian Plateau get less than the country average; the Northern Thracian Plain is often subject to summer droughts. Higher elevations, which receive the most rainfall in the country, may average over 2,540 millimetres (100 in) per year.

The many valley basins scattered through the uplands have temperature inversions resulting in stagnant air. Sofia is located in such a basin, but its elevation (about 530 metres / 1,739 feet) tends to moderate summer temperature and relieve oppressive high humidity. Sofia is also sheltered from the northern European winds by the mountains that surround its troughlike basin. Temperatures in Sofia average −3 °C (26.6 °F) in January and about 28 °C (82.4 °F) in August. The city's rainfall is near the country average, and the overall climate is pleasant.

In summer, temperatures in the southest Bulgaria often exceed 40 °C (104 °F) but remain cooler by the coast. The town of Sadovo, near Plovdiv, has recorded the highest known temperature: 45.2 °C (113.4 °F). The recorded absolute minimum temperature of −39.3 °C (−38.7 °F) occurred west of Sofia, near the town of Trun. The usual temperature around the Stara Planina region averages 10 °C (50 °F) to 15 °C (59 °F).

The highest mountains – over 900 or 1,000 metres (2,953 or 3,281 ft) above sea-level – have an alpine climate. The lowest parts of the Struma and Maritza river valleys are subjected to subtropical (Mediterranean) influence, as are the Eastern Rhodope or Low Rhodope mountains. The extreme south-west part of Bulgaria (near the towns of Sandanski and Petrich) has one of the warmest climates in the country.

The coastal climate is moderated by the Black Sea, but strong winds and violent local storms are frequent during the winter. Winters along the Danube River are bitterly cold, while sheltered low valleys opening to the south along the Greek and Turkish borders may be as mild as areas along the Mediterranean or Aegean coasts.