The 29-30 November 2016 Northern Alabama Tornado Outbreak, Part 1: Radar and Vertical Profiling Observations of a Complex Supercell Mesocyclone

A severe weather outbreak impacted the southeastern United States on 29-30 November 2016. The outbreak was responsible for nearly forty tornadoes and six direct fatalities across the southeastern United States. The Tennessee Valley region was the most severely impacted area of the outbreak, with ten confirmed tornadoes (five of which were strong EF2-EF3 tornadoes on the Enhanced Fujita Scale) and four direct fatalities. The University of Alabama in Huntsville's (UAH) Severe Weather Institute - Radar and Lightning Laboratories (SWIRLL) conducted severe weather operations within the central and eastern portions of Northern Alabama, with the UAH Mobile Integrated Profiling System (MIPS; 915 MHz wind profiler, X-band profiling radar, microwave profiling radiometer, ceilometer) located at UAH-SWIRLL in Huntsville and the C-band Advanced Radar for Meteorological and Operational Research (ARMOR) located 14.4 km away at the Huntsville International Airport.

Between 0315-0330 UTC on 30 November, a supercell with a history of producing several tornadoes, including simultaneously-occurring tornadoes with partner parent circulations, passed directly over the MIPS, surface instrumentation, and disdrometers. The X-band profiling radar’s (XPR) high-resolution vertical sampling of the supercell as it passed over the MIPS revealed an impressive time-height section of the supercell’s bounded weak echo region, mesocyclone, and rear-flank downdraft. The XPR W observed a maximum updraft of 15 m s^-1 within the mesocyclone and a maximum downdraft of 10 m s^-1 within the RFD of the supercell. At the surface a 4 C reduction in temperature, a transient 3 hPa reduction in pressure, a 360 rotation of the wind vector, and wind speed ranging from 1-18 m s^-1 was measured during passage of the circulation. Approximately 15 minutes after passing over UAH-SWIRLL, tornadogenesis occurred producing an EF-2 tornado that persisted for 32.2 km, extending from eastern Huntsville into Jackson County, AL. This presentation will investigate the storm-scale structure and environment of the tornadic supercell up through being sampled by both the UAH MIPS and ARMOR. The evolution of the supercell from having a single tornadic circulation to multiple simultaneous circulations will be discussed. Observations of the pre-tornadic mesocyclone from the MIPS will detail the near-storm and inflow environment of the supercell as well as the vertical structure of the supercell. Consequences of the MIPS observations on the theory of the structure and dynamics of supercell thunderstorms will be presented.