Hail climatology in Serbia

ABSTRACTThis study investigates the spatial and temporal characteristics of hail frequency in Serbia during the period 1949–2012. Two areas covering the whole territory of Serbia are treated: a complex terrain area (CTA) and a flat terrain area (FTA). Our research shows that the highest hail frequencies were found in the southwestern mountainous part of the country in the warm season. In the cold season, the area of maximum hail frequency lies in the region of the Sava and the Danube rivers. During the warm season, the highest hail frequencies are recorded in May and June and the smallest in August and September. This spatial pattern is influenced by the passages of the prevailing fronts, surface air temperatures and the convection enhancement by the mountains during the year. The trends of mean hail frequency are negative, except for the FTA in the dry season (August–September) and the cold season, in which nonparametric methods do not show any trends. The highest hail frequency area does not show any trend in the warm season, but interdecadal variability is significant. In general, the CTA has a greater mean hail frequency for all treated seasons. In contrast, the FTA has a greater maximum of mean hail frequency per station in the dry (August–September) and cold seasons. Although very small, the territory of Serbia also shows other peculiarities. In the last decade, the FTA has shown a strong positive trend of mean hail frequency as opposed to the CTA. This is due to the fact that the ridge of the Azores high extended over the CTA more frequently than before 2000.