Late in the evening of May 3, 1999, a Doppler on Wheels (DOW) caught the evolution of a strong tornado as it passed near the town of Mulhall, OK. Using the GBVTD technique, the azimuthal mean dynamical quantities of the tornado have been deduced. To help in quantifying the potential structure of this tornado, a simple two-dimensional vortex stability calculation has been performed on the mean tornadic structure. Preliminary results and conclusions of these calculations are presented.