Exploring the Influence of Instability and Vertical Wind Shear on Hail Size Using Hailstone Growth Trajectory Calculations

Although hail causes over $10 billion in insured losses annually in the U.S., forecasts – and even nowcasts and warnings – of maximum hail size remain unreliable. This is problematic given that maximum hail size is a significant determinant of a storm’s damage potential. Our lack of knowledge about the environmental controls on hail size and challenges of radar-based hail sizing are primary contributors to these problems.

In this study, we begin to explore how hail size distributions – as inferred from idealized growth trajectories – vary across the CAPE-shear parameter space. We performed a suite of idealized numerical simulations of supercell storms with varying hodographs and CAPE values. Time-averaged composites of each simulation are used to drive the growth trajectories by seeding hailstone embryos of varying sizes in and around the storm. The embryos are advected using the simulated three-dimensional wind field, and growth is calculated explicitly from the simulated microphysical and thermodynamic fields. The final hailstone sizes and fallout locations are used to compare hail production in various environments. If time permits, we will present preliminary experiments with growth trajectories driven by evolving storms that explore non-steady-state effects on hail growth.