Mesoscale and Stormscale Ingredients of Tornadic Supercells Producing Long-Track Tornadoes in the 2011 Alabama Super Outbreak

This study focuses on the environmental and storm scale dynamics of supercells that produce long-track tornadoes, with modeling emphasis on the central Alabama storms from April 27, 2011 - part of the 2011 Super Outbreak. While most of the 204 tornadoes produced on this day were weaker and short-lived, this particular outbreak produced 5 tornadoes in Alabama alone whose path-length exceeded 50 documented miles. The results of numerical simulations are inspected for both environmental and storm-scale contributions that make possible the formation and maintenance of such long–track tornadoes.

A two-pronged approach is undertaken, utilizing both idealized and real data simulations of the Alabama outbreak with the Weather Research and Forecasting [WRF] Model. Idealized simulations will help isolate environmental contributions, such as instability and shear, to long-track tornadic storm structure. Properties of simulated soundings, for instance hodograph length and curvature, 0-1km storm relative helicity [SRH], and buoyancy properties are compared to idealized soundings described by Adlerman and Droegemeier 2005 in an effort to identify properties conducive to storms with non-cycling mesocyclones.

Real-data simulations will model the mesoscale forcing and environmental changes along storm tracks. Uncertainty about the possible steady-state nature of inflow characteristics and storm structures of long-track tornado sustaining storms, such as the Tuscaloosa cell³, will be investigated. Model soundings are examined from the inflow of simulated storms in order to diagnose and understand favorable environments and any changes present within them in which the storms may have developed and been sustained. Additional analysis focuses on identifying and investigating mesoscale boundaries and possible storm scale vorticity structures that may have played a role in intensifying and/or sustaining the tornadic cells.

³Karstens, C. (2012). Iowa State University. Analysis of Tornado-Induced Tree-Fall using Aerial Photography from the Joplin, MO and Tuscaloosa-Birmingham, AL Tornadoes of 2011. Manuscript to be submitted for publication.