Evolution of the 4 May 2007 Greensburg, Kansas tornadic supercell storm as inferred from mobile, X-band Doppler radar observations

After producing four relatively weak (EF-0 and EF-1) tornadoes, the 4 May 2007 Greensburg, Kansas supercell storm (hereafter “the Greensburg storm”) produced an EF-5 tornado that severely damaged the town of Greensburg, Kansas. Volumetric Doppler reflectivity and velocity data were collected in the Greensburg storm by a mobile, X-band Doppler radar (UMass X-Pol) throughout this period (0126 – 0236 UTC on 5 May 2007). UMass X-Pol had a radial resolution of 150 m, and was able to detect both pretornadic and tornadic circulations in the Greensburg storm, including at least two satellite tornadoes of the Greensburg tornado. It will be shown, among other things, that (1) the Greensburg tornado originated from a remnant circulation associated with an earlier tornado, (2) the Greensburg tornado moved in the same direction as the Greensburg storm, more so than any of the earlier tornadoes, (3) the Greensburg tornado contained both a weak-echo hole and a low-ZDR hole, which are consistent with previous UMass X-Pol tornado observations, and (4) “elbows” occasionally appeared in an otherwise-smooth reflectivity spiral structure around the Greensburg tornado, possibly indicating instability in the mesocyclone. Comparisons with reflectivity and velocity data from the National Weather Service WSR-88D at Dodge City, Kansas (KDDC) will also be made.