Late March warm frontal convection in Iowa

A strong system brought severe storms to many parts of the U.S. yesterday, including a few riding along a warm front in Iowa.

The NOAA/CIMSS ProbSevere model was recently updated to include total lightning data. The total flash rate (flashes/min) is coupled with the RAP effective bulk shear to form a two-dimensional predictor. The RAP MUCAPE, MRMS MESH, and GOES-derived satellite growth rates are also still predictors in ProbSevere (see how the MUCAPE and effective bulk shear are used in ProbSevere) .

The highlighted storm in central IA developed in an environment with decreasing MUCAPE (1000 J/kg --> 600 J/kg) but excellent shear (~45-50 kts). The strong total flash rate (~35-70 fl/min) with the strong shear, as well as an observed moderate normalized growth rate, helped elevate the probability despite modest MESH (0.45-0.75 in). The probabilities ranged from 60% to 85% (mainly > 70%) before the first severe thunderstorm warning was issued, at 23:58Z, which was 5 min before the first 1" hail report.

In this case, the total lightning / effective shear predictor helped contribute to over 60 min of lead-time from the 60% threshold.

As this storm was diminishing, a conglomerate of convection erupted just to its east, producing wind and hail reports in the Des Moines metro.