Exceptionally heavy rainfall in Karlovo valley

Exceptionally heavy rainfall are one of the most difficult and challenging problems for forecasters. The synoptic situation at the beginning of September 2022, which led to significant precipitation in the Karlovo valley, was analysed. 24-hour rainfall amount of more than 200 mm were recorded, which is an event exceeding the climatic precipitation characteristics established for the region, including the rare events. The synoptic situation was based on a cyclogenesis in the Gulf of Genoa, and cyclone which passed through the southern regions of the Balkans towards the Black Sea. The precipitation is related to the formed convergent zone over Bulgaria and to the divergence on the 200/300 hPa level. Comparison with the monthly rainfall amount in the area of Karlovo as a climate showed almost 4 times exceeded values for 24-hours. The environmental conditions for development of heavy rainfall over Bulgaria was investigated using proximity sounding obtained by the numerical model GFS. Several instability indices (CAPE, Lifted index, K index, Total-Total index and etc.) and vertical wind shears between various layers are analysed in order to verify their ability to forecast rainfall. Their skill to predict severe storm types is evaluated by calculation of probability of detection (POD) and false alarm ratio (FAR). The data at the surface necessary for the calculations of the instability indices are taken from synoptic stations of National Institute of Meteorology and Hydrology (NIMH) located in centralen Bulgaria.