On 10-11 April 2001, numerous tornadic and severe thunderstorms occurred across the central U.S. Radar signatures with these fast-moving storms were small and/or weak, and this was certainly the case in Iowa on the afternoon of 11 April 2001.

This presentation will focus upon the different low-topped storm structures along a line of tornadic and severe thunderstorms in central Iowa. The small storms, some supercells, lacked strong or clear-cut radar signatures due to radar and/or range limitations, making the warning decision process extremely difficult. WSR-88D mesocyclone and tornado detection algorithms produced very few detections, and were of little help to the warning meteorologists.

The operational impacts of issuing tornado warnings for multiple non-classical storms, moving at 25 ms-1, will be highlighted. The presentation will also attempt to answer the question "What does the warning meteorologist use to make critical warning decisions when radar signatures are lacking?"

Analysis of this event was performed on the National Weather Service's new Weather Event Simulator. The authors are willing to present this case as a Simulator demonstration at the conference, or assist others in doing so.