Sampling Issues Associated with the Evansville Tornado and other nearby Supercells on the Early Morning of 6 November 2005: Challenges to Operational Forecasters

In the early morning hours of 6 November 2005, two tornadoes which caused F3 damage touched down within minutes of each other in western Kentucky. One tornado moved into southwest Indiana, through the southern end of the city of Evansville, producing a continuous damage path of 66 km. A second tornado was located 64 km to the south and produced a damage path of just less than 18 km. The tornadic and other nearby non-tornadic supercells evolved in a high shear, low convective available potential energy environment across the lower Ohio Valley region and moved at speeds up to 31 m s-1. A westerly mid-level jet was identified by the velocity azimuth display wind profiles of both the WSR-88D radar at Paducah, Kentucky (KPAH) and the Doppler radar near Evansville, Indiana (KVWX). As the mid-level jet impinged upon the supercell clusters, rotation dramatically increased and tornadogenesis rapidly occurred.

The storms which produced the tornadoes were sampled by four WSR-88D Doppler radars, yet due to storm speed, tilt, and other sampling issues, the true location and strength of the mesocyclones associated with the tornadoes were not always clear to the radar warning meteorologists. The northern storm, or the Evansville supercell, challenged warning forecasters in attempting to determine the location of the mesocyclone, which was different depending upon which radar was being used. The southern tornadic supercell moved essentially parallel to the radar beam from the KPAH WSR-88D which indicated a low-level gate-to-gate shear value of approximately 27 m s-1. At the same time, this supercell was moving generally perpendicular to the radar beams from the Hopkinsville, Kentucky (KHPX) WSR-88D which showed the presence of a low-level gate-to-gate shear of at least 51 m s-1.

This presentation will briefly describe the near storm environment which the tornadic supercells evolved from. This will be followed by a more detailed overview of the storm reflectivity and mesocyclone signatures and the sampling issues warning forecasters encountered that morning. It is hoped that this presentation will provide insights to the radar sampling challenges forecasters may experience during a dynamic cool season tornadic event and emphasize the importance of nearby radars in determining tornado potentia