Investigating Hail Melt Using ­­­Airbourne Observations and Concurrent Surface Observations of Hail

The South Dakota School of Mines & Technology flew an armored T-28 aircraft outfit with a Laser Hail Spectrometer through hail producing storms from 1995 to 2003 in Colorado, Oklahoma, and Kansas. Flying between 0° and -12°C, the T-28 was able to measure hailstones between 0.45 and 5 cm in diameter prior to significant melting. This dataset also contains estimates of vertical motion, reflectivity, hail fall speed, and kinetic energy. Surface observations of hail are available for several of these flights through the archives maintained by NOAA’s Storm Prediction Center and the Community Collaborative Rain, Hail, & Snow Network (CoCoRaHS). Together these datasets provide a glimpse of how the in-cloud hail distribution relates to the hail distribution at the surface.

A modified one-dimensional melting-only version of HAILCAST, the hail trajectory model, is developed. We will use this model to simulate how the full hail size distribution, observed during the T-28 flights, melts as the stones fall the surface. For each flight an ensemble of HAILCAST simulations is run. These ensembles are created by varying the assumed vertical velocity in the storm, assumed environmental conditions, assumed melting relationships, and how terminal velocity is calculated. Comparison of these ensembles with the surface observations is used to both gain understanding in how hail melts within clouds and below cloud base as well as better constrain how these processes are represented in HAILCAST. Ultimately, the knowledge gained from this work will be used to aid passive satellite algorithms that detect hail. Passive satellites detect hail aloft and current algorithms do not consider melting, thus, creating a dichotomy between satellite and surface-based observations.