The LaGrange Tornado during VORTEX2. Part II: Photogrammetric Analysis of the Tornado Combined with Dual-Doppler Radar Data

Abstract

Abstract This study presents the synthesis of dual-Doppler and cloud photography data of the 5 June 2009 Goshen County, Wyoming, tornado observed during the Second Verification of the Origins of Rotation in Tornadoes Experiment (VORTEX2). Analyses focused on the hook region of the parent supercell. It will be shown that radar-determined tornadogenesis and initial surface wind damage occurred 14 min before the funnel cloud was observed continuously on the ground. In addition to the cyclonic wall cloud, an anticyclonic lowering was also observed on the southern flank of the hook echo near the time of tornadogenesis. The relationship between the intensities of the tornado and its parent circulation, the low-level mesocyclone, will also be discussed. Funnel diameter was not well correlated with the maximum vertical vorticity or circulation associated with the mesocyclone. Furthermore, changes in the minimum reflectivity observed in the tornado-scale weak echo hole (WEH) were weakly correlated with the maximum vertical vorticity of the mesocyclone. The tornado funnel was observed within and was relatively small compared to the WEH diameter. The distribution and evolution of angular momentum were also examined. The radial increase of angular momentum terminated at or beyond the wall cloud edge. Prior to the time that the funnel made continuous contact with the ground, low-level angular momentum increased despite the fact that azimuthally averaged low-level flow within the mesocyclone was divergent, advecting low angular momentum air away from the circulation center. Both the tornado and mesocyclone generally intensified during this time. Thereafter, while the tornado continued to intensify, angular momentum within the low-level mesocyclone weakened.