Surface observations of the rear-flank downdraft evolution associated with the Aurora, NE tornado of 17 June 2009

On 17 June 2009 a supercell with “classic” structure produced numerous tornadoes in the Grand Island and Aurora, NE area. The rear-flank downdraft (RFD) outflow and tornado proximity environment were sampled for extensive periods by a mobile mesonet deployed as part of the Tactical Weather-Instrumented Sampling in/near Tornadoes EXperiment (TWISTEX). Of particular interest, the mesonet collected a long-duration dataset within the RFD outflow and along/near the RFD gust front preceding and concurrent with the most prominent tornado episode from this supercell. Given generally slow storm motion, part of the mobile mesonet maintained roughly similar storm-relative positions through most of the tornado lifecycle (that lasted approximately 20 min), allowing the opportunity to examine RFD outflow evolution. There were at least two RFD internal surges with this event that visually appeared to coincide with tornadogenesis and tornado intensification, respectively. The mesonet sampled the first surge and perhaps part of the second surge. Data collected on the edge of the tornado from a Hardened In-Situ Tornado Pressure Recorder probe (which also records temperature and relative humidity) may allow a thermodynamic comparison between parcels being ingested into the tornado and parcels residing in the bounding RFD outflow. Detailed analysis of this event will be presented.