Elevated September Storms

Thunderstorms developed in southern Iowa early Monday morning along a warm frontal boundary. The MLCAPE was 0 J/kg, while the MUCAPE across the baroclinic zone was 800-1000 J/kg, indicating that these storms were not rooted at the surface. The effective bulk shear was also considerable, at 45-50 kts. The storm featured below had strong satellite growth rates at 11:15 and 11:30 UTC, which contributed to an elevated probability of severe (44%) when the MRMS MESH was less than 0.5". The ProbSevere model showed probabilities increase to 84% (12:04 UTC) and 96% (12:14 UTC), as the MESH increased to 0.81" and 1.27". This storm was never warned, while one-inch diameter hail was recorded in Appanoose county, IA at 12:55 UTC, 51 minutes after the first probability of severe greater than 80%. This example demonstrates the utility of the ProbSevere model in perhaps giving forecasters a "heads-up" on storms to watch in a set-up where severe weather was not expected.

John Cintineo

UW-CIMSS