Characterizing hail-prone environments using convection-permitting reanalysis and overshooting top detections over south-central Europe

Abstract

Abstract. The challenges associated with reliably observing and simulating hazardous hailstorms call for new approaches that combine information from different available sources, such as remote sensing instruments, observations, or numerical modeling, to improve understanding of where and when severe hail most often occurs. In this work, a proxy for hail frequency is developed by combining overshooting cloud top (OT) detections from the Meteosat Second Generation (MSG) weather satellite with convection-permitting SPHERA reanalysis predictors describing hail-favorable environmental conditions. Atmospheric properties associated with ground-based reports from the European Severe Weather Database (ESWD) are considered to define specific criteria for data filtering. Five convection-related parameters from reanalysis data quantifying key ingredients for hailstorm occurrence enter the filter, namely: most unstable convective available potential energy (CAPE), K index, surface lifted index, deep-layer shear, and freezing level height. A hail frequency estimate over the extended summer season (April–October) in south-central Europe is presented for a test period of 5 years (2016–2020). OT-derived hail frequency peaks at around 15 UTC in June–July over the pre-Alpine regions and the northern Adriatic sea. The hail proxy statistically matches with ∼62 % of confirmed ESWD reports, which is roughly 22 % more than the previous estimate over Europe coupling deterministic satellite detections with coarser global reanalysis ambient conditions. The separation of hail events according to their severity highlights enhanced appropriateness of the method for large-hail-producing hailstorms (with hailstones diameters ≥ 3 cm). Further, signatures for small-hail missed occurrences are identified, which are characterized by lower instability and organization, and warmer cloud-top temperatures.

Data Driven Prediction of Severe Convection at DWD. An Overview of Recent Developments

“…For the moderate convection the clouds needs to be colder, in detail greater than 0.7 for the difference in the water water channels (WV063 − WV073 > 0.7) and greater than 2 for the BT difference of the water vapour channel and the window channel (WV062 − IR10.8 > 2). The latter condition can be used to identify overshooting tops , which are an indicator for strong updrafts associated with severe turbulences and hail [17][18][19][20]. The occurrence of lightning data is a prerequisite for the classification of the severe level.…”

Data-Driven Prediction of Severe Convection at Deutscher Wetterdienst (DWD): A Brief Overview of Recent Developments

“…For moderate convection, the clouds need to be colder, i.e., greater than 0.7 for the difference in the water channels (WV063 − WV073 > 0.7) and greater than 2 for the BT difference in the water vapor channel and the window channel (WV062 − IR10.8 > 2). The latter condition can be used to identify overshooting tops, which are an indicator of strong updrafts associated with severe turbulence and hail [17][18][19][20]. The occurrence of lightning data is a prerequisite for the identification of the severe level.…”