An Evaluation of the Potential Impact of SAILS on the Warning Decision Making of the 31 May 2013 El Reno, OK Storm

On 31 May 2013, a cluster of storms formed in west-central Oklahoma in the late afternoon and produced large hail, damaging tornadoes, and flash flooding as they moved into the Oklahoma City metro area in central Oklahoma. One tornado near El Reno, OK reached 2.6 miles in width, making it the largest tornado on record (OUN NWS Forecast Office Event Summary http://www.srh.noaa.gov/oun/?n=events-20130531). The El Reno storm featured rapid intensification of hail core signatures and tornado signatures which were well sampled by numerous operational and research radars. In this event, the KOUN WSR-88D research radar in Norman had been upgraded to include the Supplemental Adaptive Intra-Volume Low-Level Scan (SAILS; Ice et al., 2014), while the nearby operational KTLX WSR-88D did not have SAILS. SAILS provides an extra low-level scan mid-way through the volume scan, and it is particularly useful at better resolving rapidly evolving low-level features such as those observed in this event. The close proximity of the two WSR-88D radars affords a unique opportunity to compare radars and evaluate the potential impact of this new capability on the warning decision making for this storm.

This study documents the entire life cycle of the El Reno storm, provides examples of the benefits of SAILS, and it looks at the potential impact SAILS can have on warning decision making. Some features resolved by SAILS with the El Reno storm include descending hail cores, tornado-scale rotation intensification, erratic tornado movement, tornado debris signatures, and a transient weak-reflectivity eye associated with the large tornado. Full NWS-wide deployment of SAILS is scheduled to be complete in 2014, and future enhancements are being planned to further increase the number of low-level scans (Ice et al., 2014). This study illustrates the strengths and limitations of this initial significant enhancement to the NWS warning program.