From a climatic point of view, Bulgaria represents a transitional territory between Central Europe, South Eastern Europe and the Mediterranean. The Danube shelf, remaining completely out of the influences of the latter and feeling only the negligible ones of Mt Nero, is characterized by a typical continental climate: harsh and early winters, blazing summers, short intermediate seasons. The rains, already abundant in spring, reach their maximum in June, remain abundant in the early summer months, and then decrease rapidly with the arrival of autumn. In winter, snow falls frequently and stays on the ground for a long time. Rustciuk (Ruse) records 24 snowy days a year, as many as Plevna; the number grows as we approach the Balkans (Gabrovo: 39). L’ diurnal and annual excursion is usually very marked (Plevna: 24 °, 8; Gabrovo: 21 °, 9; the averages of the extreme months are respectively: January −1.8 ° and −1 °, 0; July 23 °, 1 and 20 °, 5). From maximums to isolates of 38 ° or 40 ° we descend along the Danube to minimums of −18 ° or −20 ° Rustciuk (Ruse), while the gap becomes even more sensitive towards the West (Vidin). The average annual temperature oscillates between approximately 9 ° and 12 ° (Plevna, 125 msm marks 11 °, 2; Gabrovo, at 375 m., 10 °, 0; the averages refer to the period 1894-1928), and the rainfall remains around 650-700 mm. while the detachment becomes even more sensitive towards O. (Vidin). The average annual temperature oscillates between approximately 9 ° and 12 ° (Plevna, 125 msm marks 11 °, 2; Gabrovo, at 375 m., 10 °, 0; the averages refer to the period 1894-1928), and the rainfall remains around 650-700 mm. while the detachment becomes even more sensitive towards O. (Vidin). The average annual temperature oscillates between approximately 9 ° and 12 ° (Plevna, 125 msm marks 11 °, 2; Gabrovo, at 375 m., 10 °, 0; the averages refer to the period 1894-1928), and the rainfall remains around 650-700 mm. For Bulgaria 2016, please check softwareleverage.org.
These characters are accentuated as you move towards the NE. or towards E., as well as in Dobruja and Deli-Orman, as in the Strandža region, which climatically can be considered a continuation. The winter, except in correspondence to a narrow strip along Mount Nero (Burgaz: average annual temperature 120.8; January 2, 4; July 22, 8), becomes even more raw, the rains decrease, leaving the soil dry for months and months (less than 500 mm. in the Provadiiska Planina basin and along the Danube between Lom and Orehovo).
On the other hand, the areas that stretch to S. of the Balkans, and the less elevated of Rodope, along the Struma and the Mesta, while maintaining their summer maximums of rainfall, see accentuated, more and more as it descends towards noon, the quantity of spring and winter precipitations: and this marks the transition to the type of climate that dominates the Thracian-Macedonian coast. The Marizza constitutes a natural corridor, through which the Mediterranean influences can go almost to the reverse of the Balkans, without however penetrating very deep into the valleys that from these and from the northern slopes of Rodope push towards the center of the basin (Stara Zagora, Haskovo ). The middle river valley up to Plovdiv enjoys relatively better climatic conditions, although the temperature range always remains considerable (Philippopolis: 160 msm; average annual temperature: 12 °, 6; January 0 °, 5; July 23 °, 5; absolute maximums 38 ° -40 °, minimums from −15 ° to −20 °), the summers are just as hot as in the North of the Balkans, and the amount of rainfall is equally modest (Philippopolis: 530.6 mm). However, while in Northern Bulgaria the summer months have over 30% of the rainfall, the proportion drops to almost 20% in the southern regions.
Where the arrangement of the relief, as in the pre-Calcanic valleys, allows shelter from the N and NE winds, there are oases of milder climate: fruit trees, gardens, and above all the cultivation of vines are already a clue. Both in the Balkans and on the Rila, Pirin and Rodope, wherever snow falls and the influence of height is felt, there is a real alpine climate. The passage is marked in a certain way by the SO tectonic basins. In Sofia, which rises to 550 m. height, there is an annual average of 10.0, between extremes ranging from 35 ° or 37 ° to −20 ° or −22 ° (January averages -1 °, 9, July 20 °, 7), while rainfall is increasing somewhat (Varna 470 mm., Sofia 624.7 mm.), which however does not seem to exceed 1500 mm in any district, not even the highest.
The conditions of cloudiness, relative humidity and prevailing winds in Bulgaria have not yet been studied, as one would like. In general, the former does not seem very impressive. Sofia’s annual averages (5.6) can be taken as an index of most of the other stations. The relative humidity is a little more varied from area to area, which in summer is significantly reduced: the annual values oscillating between 69 and 76 for Sofia, between 70 and 79 for Plovdiv, settle at 78-80 for Burgaz and Varna. In the winds the prevalence belongs to the West, NW directions. and it’s.; characteristic is the so-called black wind, which blows with great violence in the spring in the eastern regions.