Rapid-scan, polarimetric, mobile, Doppler-radar observations of the formation, evolution, and structure of the El Reno tornado of 31 May 2013

On 31 May 2013, the mobile Rapid-scan, X-band, Polarimetric (RaXPol) radar collected a high spatial and temporal resolution dataset documenting the genesis and intensification of a tornado that caused at least EF-3 damage near El Reno, OK; in addition, significant and rapid (e.g., O(10s)) changes to the internal structure of the tornado were documented. The RaXPol mobile radar was deployed three times during the tornadic phase of this storm, within 11 km of the center of the tornado, and collected 360 degree PPI scans at 15 meter range resolution, every 2 seconds from 0-5 degrees above radar level. It is seen from the polarimetric and Doppler data that the tornado grew rapidly to an unprecedented width, and that the tornado appeared to undergo at least one transition from being characterized by primarily a single vortex structure to a multiple vortex structure with subvortices clearly resolved in the data. As many as six vortices co-existed simultaneously; some having translational speeds in excess of 75 m/s and a maximum Doppler velocity within one of the subvortices of at least 135 m/s was measured. The transition of the multiple-vortex structure of the tornado back into a single vortex and an anticyclonic tornado developing along the rear-flank gust front were also documented in the Doppler velocity and co-polar cross correlation coefficient fields.