Mobile mesonet observations of the rear-flank downdraft evolution associated with a violent tornado near Bowdle, SD on 22 May 2010

There are many unresolved issues regarding tornadogenesis in supercells. One question that has received attention in the research community is the role of the rear-flank downdraft (RFD) and rear-flank downdraft gust front (RFDGF) in the tornadogenesis and maintenance process. TWISTEX (Tactical Weather-Instrumented Sampling in/near Tornadoes EXperiment) is an experiment designed to collect and analyze near-surface data in the RFD/RFDGF regions and in tornadoes.

On 22 May 2010, the TWISTEX mobile mesonet intercepted a tornadic supercell south of Mobridge, South Dakota. Teams followed the storm northeast as it cycled, collecting high-resolution data within multiple RFDs and associated RFDGFs over a 2 hour period. Data collected on this day includes an approximately 30 minute long RFD sampling period in close proximity to an EF-4 tornado which passed near Bowdle, SD.

An analysis of the high-resolution kinematic and thermodynamic data will be presented, and the implications for tornadogenesis and maintenance will be discussed, including:

• The thermodynamic and kinematic characterization and time evolution of the RFD associated with the EF-4 Bowdle tornado, including internal RFD gradients and multiple kinematic surges within the RFD. Teams also sampled the RFD in the post-genesis but rapidly strengthening phase of this tornado.

• A comparison of the thermodynamic and kinematic characteristics of various RFD surges throughout the first several hours of the storm's life. Other RFD samples from this storm included an initial non-tornadic RFD, and the RFDs associated with two other tornadic cycles both immediately prior to, and following the Bowdle tornado.