A Review of Near Storm Environmental and Storm Structure Characteristics of Thunderstorms that Resulted in False Alarm Tornado Warnings Across Central and Eastern Iowa

The National Weather Service's (NWS) mission is to protect the life and property of American citizens. One of the most important ways the NWS achieves this mission is by issuing crucial, life-saving tornado warnings. Recent NWS service assessments have revealed that the high false-alarm rate (FAR) of tornado warnings has resulted in complacency and non-responsiveness by the public. A FAR is defined as a tornado warning that was issued but was not verified with a reported tornado. A comparison of tornado events and FAR tornado warnings' near storm environment (NSE) and storm structure across the NWS Des Moines and NWS Davenport warning areas was conducted.

The NSE data were collected using the Storm Prediction Center's mesoscale analysis data which was originally based on merging an objective surface analysis and the latest 40 km RUC. The RUC has more recently been replaced with the Rapid Refresh (RAP) model. Examination of fourteen NSE parameters commonly used to assess tornadic potential found low level kinematic predictors such as 0-1-km shear and effective storm relative helicity in addition to mixed layer lifting condensation levels were superior discriminators between tornadic and FAR events. Events were finally filtered by storm type with a vast amount of the FAR events occurring with either quasi-linear convective systems or high precipitation supercell to bow echo transition cases. In addition, supercell mesocyclone characteristics including rotational velocity, depth and width were analyzed. These results are compared and contrasted using graphical displays and statistical techniques.