Radar-based severe storm climatology for Austrian complex orography related to vertical wind shear and atmospheric instability

Abstract The paper examines the temporal and spatial distribution of intense convective cores as a function of CAPE and vertical wind shear. C band weather radar data are exploited over the complex orography of Austria. Further ERA-Interim data are used for the classification of synoptic flow and instability. A 5-year period of convective seasons shows the presence of severe thunderstorms over Austria. The spatial distribution of high radar reflectivity differs from the radar derived precipitation field due to the contribution of stratiform rain, weak convective events, and radar related measurement errors. Westerly and southerly flow classes are associated with more widespread thunderstorm development. One of the key results is that the strong deep-layer shear environment leads to organized, line oriented pattern over wide areas of Austria, except the observed minima over the Alpine crest. These preferred areas for severe storm occurrence can be well used for nowcasting. Especially during low CAPE conditions the magnitude of deep-layer shear is very important for the spatial arrangement, maximum size of the convective system, and time of occurrence. For the eastern part of Austria and the Alps, high deep-layer shear tends to produce larger cell cores in terms of high radar reflectivity. For the Alps during low CAPE conditions and for the eastern part of Austria for all CAPE classifications, the strong deep-layer shear increases the frequency of severe storms and shifts the peak of occurrence from afternoon toward the evening.