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Abstract Most operational radar systems to date produce data with volumetric update times that are insufficient for capturing some of the rapidly evolving processes of hailstorms. Recent advances in rapid scan radar technology and innovative approaches to obtain faster scans have paved the way for a better analysis of hailstorms. This study utilizes the National Severe Storms Laboratory (NSSL)’s research Weather Surveillance Radar-1988 Doppler (WSR-88D) S-band radar, KOUN, located in Norman, Oklahoma, to examine rapidly evolving polarimetric features in hailstorms. Quantities such as rate of hail descent and changes in the updraft can be calculated through the analysis of these rapidly evolving polarimetric features, which can increase forecaster confidence in hailstorm evolution and hail sizing. Multi-Radar Multi-Sensor (MRMS) system products were generated using KOUN data, which captured the full life cycle of a hailstorm, including the cyclic evolution of hail production and its relation to tornado production. These data were compared to KTLX, located in Oklahoma City, Oklahoma, to explore what features would not be resolved without a rapid-scanning radar system. Rapid-scanning radar observations provided more details on storm-scale processes related to hail, which can aid in operational forecasting and give insight into future operational phased array radar benefits. 

Abstract Hailstone growth results in a variety of hailstone shapes. These shapes hold implications for modeling of hail processes, hailstone fall behaviors including fall speeds, and remote sensing signatures of hail. This study is an in-depth analysis of natural hailstone shapes, using a large dataset of hailstones collected in the field over a 6-yr period. These data come from manual measurements with digital calipers and three-dimensional infrared laser scans. Hailstones tend to have an ellipsoidal geometry with minor-to-major axis ratios ranging from 0.4 to 0.8, and intermediate-to-major axis ratios between 0.8 and 1.0. These suggest hailstones are better represented as triaxial ellipsoids as opposed to spheres or spheroids, which is commonly assumed. The laser scans allow for precise sphericity measurements, for the first time. Hailstones become increasingly nonspherical with increasing maximum dimension, with a typical range of sphericity values of 0.57 to 0.99. These sphericity values were used to estimate the drag coefficient, which was found to have a typical range of 0.5 to over 0.9. Hailstone maximum dimension tends to be 20%–50% larger than the equivalent-volume spherical diameter. As a step toward understanding and quantifying hailstone shapes, this study may aid in better parameterizations of hail in models and remote sensing hail detection and sizing algorithms.