engleski

Application of the WRF-HAILCAST model to the Croatian area – sensitivity to PBL schemes

The existing analysis of measurements showed that western and central regions of Croatia have the highest frequency of hail occurrence, characterized by large intensity. Due to the long history of hail suppression activities in the aforementioned regions, hailpads were placed at main meteorological stations, locations used for hail suppression activities, as well as on the specially designed polygon in the northwestern region of Croatia. Parameters that can be determined by hailpads are: (i) diameter and the number of hailstones and (ii) the kinetic energy (KE) of hailstones. Despite its frequent occurrence, hail still remains a difficult phenomenon to model or forecast as the processes involved in producing hail are not fully resolved by current convection-allowing models (CAM). One of the ways to address this issue is by embedding a physically based one-dimensional hail model called HAILCAST within a CAM. Here, the HAILCAST model is embedded within Weather Research and Forecasting (WRF) model since the WRF model, when run at a horizontal grid spacing of approximately 4 km or finer, can reproduce dominant, large-scale circulations and hydrometeor fields associated with organized storms and convective systems. Selected hail events are analyzed using the WRF-HAILCAST model simulations. HAILCAST consists of a one-dimensional steady-state cloud model coupled with a time-dependent hail growth model. The vertical updraft, liquid and ice water content, and temperature profiles from a given WRF timestep and grid columns are passed to the time-dependent WRF-HAILCAST model which forecasts maximum hail diameter at the surface. A set of numerical convection-permitting experiments are performed to assess the sensitivity of the results to five (two non-local and three local) planetary boundary layer (PBL) parametrization schemes and to provide guidance for WRF-HAILCAST tuning. The results are verified by observational (hailpad, hail observations) data as well as with radar and lightning measurements where available.

Hail, WRF-HAILCAST, PBL schemes

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