Dr. Staytcho Kolev of the Bulgarian National Institute of Meteorology and Hydrology was kind enough to respond to the post on Bulgaria from a couple of weeks ago, adding some additional insight to the climate of Bulgaria.
The four most common synoptic scale features that influence weather for the Balkans in general and Bulgaria in particular are polar cyclones, and with more frequency, those borne in the Mediterranean. Polar ridges are also a common feature for the Balkans, and the ever present Azores high also influences the climate of Bulgaria.
Dr. Kolev also wished to reassert the importance the topography of Bulgaria has in the regions climate. The Stara Planina, or Balkan Mountains, bisect the country from west to east. In the Summer and into Autumn, when systems ride at latitudes further to the north, shower activity cannot traverse the mountain ranges, and the northern parts of the country see the heaviest precipitation during this time of year. In cooler months, when the systems develop further to the south and over the Mediterranean, the opposite is true, with the rain fall getting hemmed up along the southern slopes of the Stara Planina. Along the coast, as one can imagine, the Black Sea does moderate temperatures in the harsher summer and winter seasons.
Over the past 20 years, dry Springs and Autumns have led to dry years on the whole. 2000 was the driest year of the century for Bulgaria, with only the northeastern part of the country and certain mountainous areas not seeing the aridity. Since 2000, Bulgaria has still been drier and warmer than average, but those changes have been less anomalous.
Thanks again to Dr. Kolev for taking the time to educate us further on the weather in Bulgaria!