92nd American Meteorological Society Annual Meeting (January 22-26, 2012)

Wednesday, 25 January 2012: 10:30 AM
The Dynamics and Morphology of Two Long-Track Tornadic Supercells on 27 April 2011
Room 252/253 (New Orleans Convention Center )
Timothy A. Coleman, University of Alabama in Huntsville, Huntsville, AL ; and K. Knupp and T. Murphy

There were numerous tornadic supercells on the afternoon of 27 April 2011 in the Southeast US, but two specific ones produced a large percentage of the property damage and fatalities, producing multiple violent tornadoes. The storms moved through an environment that was extremely supportive of tornadoes, with CAPE values of 2000 to 3000 J/kg, and 0-1 km SR helicity values of 500 to 700 m2/s2. This produced energy-helicity indices (EHI) near 10 units, a value rarely documented, and in this case associated with nine violent tornadoes in one state in one day. Radar data illustrate remarkable features in the two storms examined in this study, the Tuscaloosa-Birmingham tornadic storm, and the Hackleburg-Huntsville storm. These features include large rotational velocity, rotational KE, and vorticity; long hook echoes; and debris signatures. Also, both storms passed close enough to radars to allow for limited dual- or synthetic-dual Doppler analysis.

The parent storm of the Birmingham to Tuscaloosa EF-4 tornado was extremely long-tracked (over 300 km), and produced an additional long-track EF-4 tornado from northeast of Birmingham into Georgia. The storm had an extremly impressive radar presentation, including a large debris ball that changed in reflectvity depending on the land cover it was passing over. The storm passed within 50 km of the Birmingham, AL WSR-88D radar, and was fairly steady state over a 20-minute period as it moved between Tuscaloosa and Birmingham. This, along with the fast movement of the storm, allows for synthetic dual-Doppler analysis to be performed. This analysis should reveal estimates of vertical motion, including the RFD and the extreme updraft. Using this data, an attempt will be made to determine the non-hydrostatic vertical PGF associated with the initially buoyancy-driven updraft's interaction with the high-shear environment.

The supercell that produced a long-track (almost 150 km) EF-5 tornado from Hackleburg, AL through the northwestern suburbs of Huntsville, AL, was moving along a strong thermal boundary that likely added even more horizontal vorticity and effective helicity. This storm moved within the dual-Doppler lobe between the UAH ARMOR radar and the Mobile Alabama X-Band (MAX) radar (that was positioned about 50 km to the NE of ARMOR, with both radars southeast of the tornado track). Single- and dual-Doppler analysis will be performed on this storm.

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