Evaluation of an Alberta Hail Growth Model Using Severe P9.5 Hail Proximity Soundings in the United States

Forecasters currently have very few tools at their disposal to aid them in predicting the maximum expected hail size. Moreover, the few tools that are available frequently forecast unrealistically large hail sizes in high CAPE environments. Perhaps the main reason for this is that the hail growth process is very complex and consequently, any ingredients-based forecasting methods that are typically used to forecast severe weather will usually result in poor hail size forecasts, with little if any skill (Doswell et al. 1992). The complexity of hail growth is handled best by three-dimensional (3D) cloud models (e.g., Xu 1983). However, 3D models are cumbersome and impractical to run in an operational setting (Brooks et al. 1992). A simple one-dimensional model, called HAILCAST, has been developed to predict the maximum expected hail diameter (D) at the surface (Brimelow et al. 2002a). HAILCAST has been implemented and tested at the Storm Prediction Center (SPC) over the past two years. The simplicity and computational efficiency of HAILCAST makes it a practical tool for predicting the maximum hail size.