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

A severe weather outbreak impacted the southeastern United States on 29-30 November 2016 with the outbreak being 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 VORTEX-SE related 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 and the C-band Advanced Radar for Meteorological and Operational Research (ARMOR) located 14.4 km away at the Huntsville International Airport. Approximately 15 minutes after passing over the MIPS, tornadogenesis occurred producing an EF-2 tornado that persisted for 32.2 km, extending from eastern Huntsville into Jackson County, AL.

Between 0315-0330 UTC on 30 November, a supercell with a history of producing 6 tornadoes passed 5 miles south of ARMOR and directly over the MIPS, surface instrumentation, and disdrometers. The X-band profiling radar’s (XPR) high-resolution sampling (1 Hz, 50 m range gate spacing) 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, which measures vertical radial velocity (W) which is the sum of the hydrometeor terminal fall speed (V_t) and the true air motion (w), observed a maximum updraft of 21 m s^-1 within the mesocyclone and a maximum downdraft of -3 m s^-1 within the RFD of the supercell when the estimated V_t was removed. V_t was estimated by using disdrometer data at the surface and assuming a vertical continuity of hydrometers. At the surface a 4 K 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. 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. Furthermore, the thermodynamics and precipitation characteristics of the rear flank downdraft will be discussed. This includes observations from the surface of temperature reduction and potential temperature deficits within the RFD. Consequences of the MIPS observations on the theory of the structure and dynamics of supercell thunderstorms will be presented.