Gargantuan Hail Documenting an Extreme Forecasting Challenge

Abstract

I n the scientific literature, some studies have identified “giant” hail as those stones with maximum dimensions exceeding 10 cm or 4 in. We propose a new size class for hailstones with maximum dimensions exceeding 15 cm or 6 in. (referred to here as “gargantuan hail”) to represent the upper extreme of hail sizes. As these are rare cases, only a few studies have specifically documented giant and gargantuan hail events, and most are individual case studies. One study of giant and gargantuan hailstones from the Aurora, Nebraska, storm of 2003 showed that every stone evaluated exhibited an outer (i.e., final) growth layer indicating wet growth, and in some cases this layer was of quite substantial thickness. Another study used social media reports to identify giant hail that ultimately became certified state records. It suggested that the occurrence of giant or gargantuan hail is significantly underreported. None of the aforementioned studies focused on observedtorm properties or environments. In con- trast, a 2013 study documented the synoptic and mesoscale environment of the super- cell that produced the Vivian, South Dakota, hailstone (which registers as the world re- cord for maximum dimension of 20 cm or 8 in.). Analysis indicated that the environment was indeed supportive of severe convective storms, but not indicative of such large hail as was observed