Approximately 12 different RFDs (both tornadic and nontornadic) were sampled by Project ANSWERS using an array of four mobile mesonets during the late spring and early summer of 2003. One case of particular interest occurred on June 9th near Basset, Nebraska in which a weak tornado developed in very close proximity to the projects mobile mesonet array. During the 10 minute period prior to tornadogenesis, the team was deployed such that high spatial resolution data could be collected in the RFD region as the storm approached the mesonet array from the northwest. Atmospheric variables were sampled every 2 seconds.
A preliminary analysis of the high resolution data using 12 s time averages revealed several interesting features as the storm slowly passed to the north and east of the team. Two smaller RFD surges embedded within a broader RFD were detected in the mesonet array in the 10 minutes preceding tornadogenesis. The passage of the first RFD surge revealed several small vortices along the RFD surge boundary, one of which passed almost directly over one of the mobile mesonets. The second RFD surge passed through the array approximately 1-2 minutes prior to tornadogenesis. As the second RFD surge passed, a distinct small scale (~1-2 km wide) convergence/divergence couplet was detected in the mesonet array. Tornadogenesis occurred a few hundred meters to the northeast of one of the mesonets following the passage of the second RFD surge. Results and additional analysis from this case will be presented, and the possible role of RFD surges in tornadogenesis will be discussed.
Supplementary URL: http://www.windlogics.com/stormres/P11.3_SLS2004_ANSWERS_June9_RFD.pdf