Simulating Hail and Lightning over the Alpine Adriatic Region - A model Intercomparison Study

Abstract

Hail is a significant convective weather hazard, often causing considerable crop and property damage across the world. Although extremely damaging, hail still remains a challenging phenomenon to model and forecast, given the limited computational resolution and the gaps in understanding the processes involved in hail formation. Here, eight hailstorms occurring over the Alpine-Adriatic region are analyzed using Weather Research and Forecasting (WRF) and Consortium for Small Scale Modeling (COSMO) simulations, with embedded HAILCAST and Lightning Potential Index (LPI) diagnostics at kilometer-scale grid spacing (~2.2 km). In addition, a model intercomparison study is performed to investigate the ability of the different modeling systems in reproducing such convective extremes, and to further assess the uncertainties associated with simulations of such localized phenomena. The results are verified by hailpad observations over Croatia, radar estimates of hail over Switzerland and lightning measurements from the LINET network. The analysis revealed that both HAILCAST and LPI are able to reproduce the areas and intensities affected by hail and lightning. Moreover, the hail and lightning fields produced by both models are similar, although a slight tendency of WRF to produce smaller hail swaths with larger hailstones and higher LPI compared to COSMO is visible. It is found that these differences can be explained by systematic differences in vertical profiles of microphysical properties and updraft strength between the models. Overall, the promising results indicate that both HAILCAST and LPI could be valuable tools for real-time forecasting and climatological assessment of hail and lightning in current and changing climates.

Exploring hail and lightning diagnostics over the Alpine-Adriatic region in a km-scale climate model

“…Our findings show that HAILCAST and LPI integrated with COSMO are promising tools to diagnose hail and lightning over the Alpine Adriatic region (as also shown by (Malečić et al, 2023)). However, a couple of shortcomings are revealed:…”

“…For example, if updrafts are weaker, larger hail fall down faster and do not have enough time to grow further, while smaller hail have more time to grow but do not reach sizes above 20 mm. In a parallel study, in which the same eight cases are simulated with the WRF model (Malečić et al, 2023), larger hailstones are obtained with the WRF model than with COSMO. This result indicates that the simulated hail size strongly depends upon the model formulation.…”