School of Meteorology (Defense)

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

Kyle Thiem

School of Meteorology

21 October 2016, 10:00 AM

National Weather Center, Room 3620
120 David L. Boren Blvd.
University of Oklahoma
Norman, OK

On 31 May 2013, the mobile, Rapid-scan, X-band, Polarimetric (RaXPol) radar collected a high spatial and temporal resolution dataset documenting the genesis, intensification, and dissipation of a tornado that caused EF-3 damage near El Reno, OK, although Doppler velocities measured by RaXPol exceeded 135 m/s near the surface. The RaXPol mobile radar was deployed three times during the tornadic phase of this storm between 4.5-11 km from the center of the tornado, and collected 360 degree PPI scans every 2 seconds with range gate spacing between 45 meters to 15 meters.

The evolution of the Doppler-velocity field before and after tornadogenesis was analyzed to investigate the dynamics involved in the genesis process. Reconstructed vertical cross-sections taken through the center of the tornado reveal fine-scale details about the vortex structure and how it evolves throughout the tornado’s lifecycle. The tornado then grew rapidly to an unprecedented width and underwent at least one transition from a single-vortex structure to a multiple-vortex structure. Within the Doppler velocity data, multiple subvortices were resolved during the large, multiple-vortex phase of the El Reno tornado’s life cycle, over a time period of 132 seconds. Details about the origins, paths, and dissipations of at least two-dozen resolvable subvortices, some of which had translational speeds in excess of 75 m/s, were documented. The subvortices mostly developed inside the radius of maximum winds and those that persisted for longer periods of time (>15 seconds) tended to traverse towards the center of the tornadic vortex over their life cycles. Details regarding the evolution and kinematics of the subvortices were compared to composite background fields of radial velocity and spectrum width to draw conclusions regarding the areas of common subvortex genesis and dissipation. Azimuthal velocities of the subvortices will also be compared to the background radial velocity field to determine if they were retrograding with respect to the mean flow, as tornado vortex theory would suggest. Finally, a rapid transition from a large, broad vortex to a small, tight vortex observed in the Doppler velocity and cross-correlation coefficient fields will be discussed along with the simultaneous existence of an anticyclonic tornado and its connection to the rear-flank gust front.

School of Meteorology (Defense) Seminar Series website