Mobile Doppler radar observations of a tornado near Verden, Oklahoma on 3 May 1999

Using the 3-mm wavelength, mobile, Doppler radar from the University of Massachusetts, a group from the University of Oklahoma probed the early stages of a tornado whose circulation eventually developed into the Oklahoma City tornado about an hour later. With the antenna having a half-power beamwidth of only 0.18 deg, azimuthal resolution of only 5-10 m was obtained in the nearby tornado. Using the PDPP technique, a maximum unambiguous velocity of +/-79 m/s was achieved. Maximum wind speeds were found near the folding velocity. Features such as spiral bands around the tornado and transverse bands in the hook echo are described. The most intriguing aspect of this dataset is the evidence of multiple-vortex structure: Waves in the radar reflectivity field along the edge of the tornado eyewall and evidence of small-scale Doppler-velocity couplets are discussed. Maximum wind speeds detected agreed with the extent of the damage inflicted by the tornado.