Multiple Doppler Radar Analysis of External Environmental and Topographical Influences on a QLCS Tornado Event

The midday and afternoon hours of 11 April 2013 featured a severe weather episode across the southeastern United States, during which a mixed mode of discrete supercells and a quasi-linear convective system (QLCS) produced several tornadoes. A pair of EF1 tornadoes, spawned by the same mesovortex embedded within a QLCS, impacted Redstone Arsenal and the south side of Huntsville, Alabama between 2120 UTC and 2135 UTC. These tornadoes occurred within approximately 12 to 25 km of the Advanced Radar for Meteorological and Operational Research (ARMOR), within 1.5 to 18 km of the S-band Doppler weather radar located at Redstone Arsenal (RSA), approximately 25 to 40 km from the Mobile Alabama X-band (MAX) radar, and approximately 40-55 km from the Weather Surveillance Radar-88 Doppler (WSR-88D) located at Hytop, Alabama (KHTX). The two tornado tracks were separated by a mountain featuring an elevation change from approximately 195 m MSL at the base on either side of the mountain to approximately 430 m MSL at mountaintop. Additionally, wave interactions were observed with the QLCS prior to and coincident with tornadogenesis.

In this presentation, we provide a multiple-platform review of this QLCS tornado event. We review radar data from ARMOR, MAX, KHTX, and RSA, as well as data from the Mobile Integrated Profiling System (MIPS, located ~10 km north of the initiation point), which includes a vertically-pointing X-band profiling radar (XPR) as well as a 915-MHz Doppler wind profiler. This data is used in conjunction with surface data from several sites across northern Alabama, including ASOS sites at Huntsville (KHSV) and Decatur (KDCU), a surface observation site at the University of Alabama at Huntsville (UAH), and a myriad of surface observing stations at RSA, ranging from 2-105 m AGL, as well as detailed damage survey data to analyze the interactions of several wave features with the QLCS as well as the evolution of the tornadoes and the parent mesovortex as it interacted with the mountainous terrain. We evaluate past observational and numerical modeling studies of squall line evolution, of wave interactions with mesocyclones and mesovortices, and of interactions of tornadoes and parent circulations with significant terrain features and seek to compare the results of those past studies with the high resolution, comprehensive observations from the above platforms.