Evolution of low-level rotation in the tornadic 29 May 2004 Geary, Oklahoma supercell storm

Two mobile C-band Doppler SMART radars sampled a high-precipitation, tornadic supercell storm on 29 May 2004 during its severe, right-moving phase. Bulk parameters of the storm's near-environment were obtained from approximately hourly, storm-following mobile GPS advanced upper-air sounding system (MGAUS) profiles obtained within the storm's inflow extending from its initiation stage through the time of maximum low-level rotation in central Oklahoma. Analysis of the high-resolution, dual-Doppler three-dimensional airflow focuses on identifying downdraft source regions and estimating vorticity dynamical processes that contribute to the development of the low-level mesocyclonic and tornado-cyclonic circulations.

During the storm's most intense phase, a storm-scale rear-flank downdraft boundary (RFDB) intersected the conventional forward flank downdraft boundary (FFDB) within the wrapping inflow to the intensifying low-level mesocyclone. The combined dataset facilitates preliminary testing of the hypothesis that the low-level mesocyclone is intensified via the classical mechanism of solenoidal (horizontal streamwise) vorticity generation followed by tilting and stretching with contributions from both the RFDB and FFDB. The evolution of the low-level angular momentum field will also be examined as a preliminary test of the alternate hypothesis that RFD development combined with strong stratification of horizontal angular momentum may combine to trigger a corner-flow collapse process leading to low-level mesocyclogenesis. This case illustrates the likely hypothesis testing procedures for other supercell storms sampled by the SMART radars during the upcoming VORTEX2 field project.