Assessing the performance of WRF model in simulating severe hailstorm events over Assam and Bihar, India

This study investigates the performance of the Advanced Research Weather Research and Forecasting (WRF-ARW) model in simulating two severe hailstorm events. The simulation period covers the post-monsoon and pre-monsoon hailstorm events of 26 December 2022 in Assam and 19 May 2022 in Bihar, respectively, with a continuous model integration of 48 h. The WRF model is integrated on a double nested domain of 9 and 3 km horizontal resolutions using the Milbrandt 2-moment microphysical and Kain Fritsch cumulus schemes. Critical analyses include the mixing ratio of hydrometeors, maximum reflectivity, wind magnitude and direction, temperature contours, and relative humidity. The results were validated using ERA-5 reanalysis data. Instability indices such as Convective Available Potential Energy (CAPE), Total Totals Index (TTI), and Significant Hail Parameter (SHIP) are evaluated to assess the hailstorm environment. The hail mixing ratio peak between altitudes 600-700 hPa suggests a significant presence of hail in the mid-troposphere. A high-level jet was observed during the Assam event. The SHIP value calculated from the model output for the Assam event was 0.1, indicating a non-significant hail environment. In contrast, for Bihar, the SHIP value was 2.0, suggesting a significant hail environment. Despite a CAPE value of approximately 500 J/kg for the Assam event, typically not indicative of severe thunderstorms, hail occurred. The CAPE value of around 3000 J/kg in Bihar indicated severe thunderstorm conditions. The WRF could reasonably simulate both hailstorm events with the selected configuration.