Fast moving storms and MRMS MESH

A fast moving storm in west-central Illinois yesterday produced hail much larger than the expected maximum size, depicted by the MRMS MESH, part of the ProbSevere model. Though it might not look like it from the animation below, the storm was pegged moving NE at 50 mph.

In cases like these, a fast-moving storm that is also perhaps shallow can result in an underestimate of MESH, since the storm may move a non-negligible amount in between consecutive radar elevation scans, resulting in a storm that appears to have a 'tilted' core, but is really just a result of storm motion. A 'tilted' or legitimately tilted core can result in a lower than normal MESH since MESH is based off of vertical integration of reflectivity.

Despite a strong satellite growth rate, the weak MESH, weak total lightning flash rate, and weak-moderate shear only resulted in a probability of severe of 9% when a 1" hail report was received (18:35Z, 4 min before the warning was issued), and maximum probability of 27%. In this case, ProbSevere would not have been useful to highlight the hail potential, thus forecasters should bear in mind many other environmental factors as well as the limitations of observations.