Ground Observations from the In Situ Collaborative Experiment for the Collection of Hail in the Plains

Detailed ground observations of hailstones are historically rare, particularly as it relates to properties that describe hail beyond its maximum single axis diameter, or in sampling the hail swath in substantive detail. To address this gap the In Situ Collaborative Experiment for the Collection of Hail in the Plains (ICECHIP) campaign was conducted between May 15 and June 28th of 2025. Active periods of convection persisted throughout the campaign yielding over 20 intensive observation periods. These included measurement of hail in numerous storms producing 50 mm or greater hail, with both in situ measurement platforms and post-storm transects of the hailswaths sampled close to time of fall in cooled environments and regularly thereafter  at horizontal resolutions in the hundreds of meters. 

Five types of instruments focused on direct hail capture: impact disdrometers with video cameras and hailpads formed the bulk of the sensing array, deployed ahead of the storm. These were complemented by mesonet pods for near-storm environment and SUMHOs, (Super Mobile Hail Observatory) deployable instrumented supersites that funnel hail into cooled storage with colocated hailpad, and measure hailstone fall speed using vertical pointing radar. High resolution and speed video cameras additionally captured hail fall speed and orientation. These were operated in a range of array configurations to best sample storm evolution or the swath at impressive resolution. Post storm sampling accumulated thousands of hailstones, and performed 2-3 axial dimensional measurements along with mass, and for a subset of stones exceeding 2cm, compressive strength testing via crushing.

This presentation will focus on three exemplary cases, a supercell in northeast Colorado producing a 14 mile-wide swath with hail diameters reaching 90 mm, a merging supercell that produced giant hailstones measuring as large as 150mm, and a non-supercell case producing extremely soft accumulating hail. Hailstone size and sphericity distributions, compressive strength properties and mass will be compared across the respective swaths to provide preliminary insights into the variability of hail and its potential for damage under different classes of storms.