The mechanics of falling hailstones and hailswaths

Supercell thunderstorms are known to be excellent producers of large, destructive hail. ‎The strong updrafts within the thunderstorm can sustain large hailstones, many of which ‎are spheroids, and some of which can become irregularly-shaped with knobs, lobes, or ‎spikes on their surface. Such irregular surface characteristics can alter the drag coefficient ‎of hailstones, causing them to fall faster if supercritical Reynolds number flow is ‎achieved. It is one focus of this study to examine such hailstone fall conditions and ‎determine their similarity to nature. Besides these special cases of hailstones, the descent ‎of hail from a thunderstorm is also studied with respect to updrafts and downdrafts, ‎thunderstorm translational speed, internal thunderstorm rotation, turbulence, and density ‎variations of both the hail and the atmosphere. These factors determine the speed at ‎which the hailstone strikes the ground, which in turn partly determines the amount of ‎damage the hailstorm is capable of producing, along with the hailswath. ‎ In the second part of this study, given that the conditions of hail fall are known, ‎the hailstone's landing location on the ground with respect to the center of mesoscale ‎circulation will be calculated. In thunderstorms that exhibit rotation, they produce a size-‎sorted hailswath on the ground where larger hailstones land closer to the center of ‎circulation. This study examines the size-sorting effect and compares a modeled ‎hailswath to documented hailswaths. The calculation of this size-sorted hailswath may ‎have operational use in forecasting where specific warnings can be issued containing ‎detailed information about the size of hail that may reach the affected localities. ‎