1. J. Wurman, School of Meteorology, University of Oklahoma, 100 East Boyd Street, Norman, OK 73019, USA.
2. J. M. Straka, School of Meteorology, Center for Analysis and Prediction of Storms and Cooperative Institute for Mesoscale Meteorological Studies, University of Oklahoma, 100 East Boyd Street, Norman, OK 73019, USA.
3. E. N. Rasmussen, National Severe Storms Laboratory, 1313 Halley Circle, Norman, OK 73069, USA.