20 Nov 2023
 | 20 Nov 2023
Status: this preprint is open for discussion.

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

Antonio Giordani, Michael Kunz, Kristopher M. Bedka, Heinz Jürgen Punge, Tiziana Paccagnella, Valentina Pavan, Ines M. L. Cerenzia, and Silvana Di Sabatino

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.

Antonio Giordani et al.

Status: open (until 01 Jan 2024)

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Antonio Giordani et al.

Antonio Giordani et al.


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Short summary
To improve the challenging representation of hazardous hailstorms, a proxy for hail frequency based on satellite cloud top detections, convective parameters from high-resolution reanalysis, and crowd-sourced reports, is presented. Hail likelihood peaks in central summer at 15 UTC over northern Italy and shows improved agreement with observations compared to a previous estimate. Separating ambient signatures based on hail severity, enhanced appropriateness for large hail occurrence is found.