A kinematic, multiple Doppler, and dual-pol radar analysis of the mid-day tornadic QLCS during the historic April 27th super outbreak

During the historic 27 April 2011 tornado outbreak in the Southeastern U.S., three rounds of tornadic storms impacted north Alabama: 1) an early morning QLCS with multiple MCVs which produced 31 tornadoes in north and central Alabama, 2) a shorter mid-day QLCS which produced 7 tornadoes in a two county area, and 3) afternoon supercells which accounted for 31 of 36 tornadoes of EF-3 intensity or greater. The mid-day tornadic QLCS tracked within the UAHuntsville/NSSTC THOR Center and Hazardous Weather Testbed, which includes the dual-Doppler domains for the WSR-88D radar at Hytop, AL, the Advanced Radar for Meteorological and Operational Research (ARMOR) C-band dual polarimetric radar, the Mobile Alabama X-band (MAX) dual polarimetric radar, as well as atmospheric profiling measurements with the Mobile Integrated Profiling System (MIPS). Observations of this system include the rapid development of multiple low-level tornadic circulations as indicated by pronounced curls in reflectivity extending from the linear system, rotational signatures in Doppler velocity, and brief debris signatures in the dual-polarimetry from ARMOR. As the system moved directly over the MIPS site at UAHuntsville, high temporal measurements (6 Hz) of a bounded weak echo region and a strong gust front with distinct horizontal rolls were sampled by the vertically-pointing X-band radar (XPR).

Prior to the development of the low-level tornadic circulations, reflectivity tags were noted to be moving through the convective line nearly perpendicular to the linear orientation. These reflectivity tags were associated with the development of leading edge reflectivity notches which exhibited a distinct periodicity as the relatively smooth line transitioned into a line echo wave pattern. This presentation will provide a kinematic analysis of the wind shear environment and in-storm wind field during the rapid development of the low-level tornadic circulations, through the use of multiple Doppler syntheses and atmospheric profiling measurements. Analysis of low-level debris signatures from the ARMOR C-band dual-polarimetric data will also be examined. Finally, a discussion on interactions between the QLCS and atmospheric waves will be presented along with the possible impacts on QLCS structure and propagation.