The authors analyze the pretornadic (0106-0138 UTC) and genesis (tornadogenesis occurred at 0138 UTC) phases of the Clinton, Oklahoma supercell of 12 May 2010 intercepted by the Second Verification of the Origins of Rotation in a Tornado Experiment (VORTEX2). The analysis relies on radar data from a pair of Doppler On Wheels (DOW) radars, mobile mesonet observations, and mobile sounding observations.

The storm resembles tornadic supecells previously observed by DOW radars. Counterrotating vortices straddle the hook echo within the rear flank outflow, and are connected by arching vortex lines. The cyclonic vortex becomes favored, and is eventually intensified to tornadic strength. The outflow in the hook echo region, where sampled, has relatively small virtual potential temperature deficits. The formation of a primary gust front along the forward edge of the outflow precedes the occluded stage of the supercell storm.

Preexisting low-level rotation is strongly weakened by the arrival of a descending reflectivity core (DRC) at the surface in the 0122-0126 UTC time period, and consequently the main storm updraft abates. By 0128 UTC, a new updraft develops along the leading edge of the gust front, followed by the tilting and stretching of baroclinically-generated horizontal vorticity to tornadic strength at 0138 UTC. As has been observed in recent studies, the DRC is associated with a rapid increase in vertical vorticity and circulation, although the documentation of this type of DRC is limited. It is becoming apparent that the DRC may have dynamic effects on tornadic evolution that are not yet understood.