Observations on the Origins of Rotation: The Newcastle Tornado during VORTEX 94

Observations of a strong (F3) tornado near Newcastle, Texas, on 29 May 1994 during the Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX) are presented. The visual characteristics and intensity of the tornado were revealed by a photogrammmetric analysis of pictures taken by chase teams and by a detailed damage survey. The tornado developed from a low-level shear feature along the flanking line of a supercell. Vortex stretching of this feature to tornadic intensity occurred under the influence of an intense updraft from a rapidly growing storm along the flanking line. No apparent midlevel mesocyclone accompanied this tornado. In contrast, the supercell was characterized by a well-defined mid- and low-level mesocyclone; however, no tornado was observed by ground chase teams. The implications of these findings on the current understanding of tornadogenesis are discussed.