A Mini-Supercell Observed During an Outbreak of Classic Supercells on 9 May 2013

During the afternoon of May 9, 2016, a scattered line of supercells formed along a dryline in western Oklahoma and produced a regional outbreak of tornadoes and other severe weather.  Embedded between two of the large-strong-tall classic supercells was a smaller storm recognized after-the-fact as a mini-supercell (near Mill Creek, OK).  The classic supercell to the north (Katie-Sulphur storm) produced an EF4 and an EF3 tornado.  The classic supercell to the south (Bromide-Atoka storm) produced an EF3 and a high-end EF1 tornado.  The Mill Creek storm produced only an EF0 tornado, but occurred in a very rural area with few structures to potentially be damaged.  Television station helicopter footage (shown live, both locally and nationally) revealed a substantial vortex likely capable of inflicting more significant damage.  This paper will document the rather innocuous mid-range-from-the-radar (~100 km) character of the Mill Creek WSR-88D (KTLX) vortex signature when compared to the closer-to-the-radar (~20 km) character of the vortex signature from a research radar (RaXPol).  Based on the modest operational radar signature and the context of the regional outbreak, the paper will discuss the difficulties in warning on the Mill Creek storm.  The paper will also ask questions about possible mesoscale environmental characteristics and storm interactions that could result in the somewhat-unusual case of a mini-supercell forming between two classic supercells.