High-Resolution Observations of the Pre-Storm Boundary Layer and Internal Structure of a Prefrontal Tornadic Cool Season QLCS Using Multiple Atmospheric Profiling Systems and Dual Doppler Radar

On 18 November 2017 a tornadic QLCS produced at least 14 tornadoes, including 5 EF0, 7 EF1, and 2 EF2 tornadoes, as well as two vortex tracks of sub-EF0 intensity over northern Alabama. As the QLCS moved into northwestern and northern Alabama, it rapidly evolved to a wavy structure with two primary embedded mesovortices within which the tornadoes formed. Four tornadoes, and one subtornadic vortex, were sampled within a high-resolution dual Doppler network, consisting of the Mobile Alabama X-band and ARMOR C-band radars separated by 18 km. Over this same domain, multiple profiling systems, including the Rapidly Deployable Atmospheric Profiling System (RaDAPS) and the Mobile Doppler Lidar and Sounding system (MoDLS) at UAH, which collectively included a 915 MHz wind profiler, Doppler wind lidar (DWL), X-band profiling radar, two profiling radiometers, and two balloon soundings; and the CLAMPS-2 (DWL, AERI, and profiling radiometer) located 22 km west of UAH, adjacent to the primary dual Doppler lobe. In addition, one mobile mesonet (Mobile Meteorological Measurement Vehicle, M3V) and a variety of surface stations provided targeted samples of an MV and associated tornadoes within the dual Doppler network

The scientific objectives of this study include the following:

• Define the changes in co-evolving boundary layer (BL) thermodynamic and kinematic properties as the QLCS moved into the observational domain. This QLCS entered the dual Doppler and profiler network during the afternoon to evening transition, and cloud shading and evaporation of rain in a narrow band immediately ahead of the QLCS produced additional BL stabilization. The second sounding was released into this precipitation as low-level mammatous formations, suggestive of an elevated instability produced by differential evaporation in the vertical, moved over the UAH location where vertically-pointing radar observations show impressive fine scale structures above the pre-storm BL. In addition, variance of vertical motion provided by the DWLs shows a decrease in BL turbulence at both the CLAMPS-2 and MIPS locations. The corresponding increase in vertical shear and SRH is documented at the two profiling sites, and at the MAX and ARMOR radars sites using high-resolution VAD analyses.
• Examine the kinematic structure of the QLCS, including the range of circulations (four tornadoes and one subtornadic vortex) along with the parent mesovortices that were observed with single Doppler radar, and resolvable with dual Doppler radar analyses. This analysis will include a characterization of a synoptic scale cold front that trailed the QLCS, and relate surface features within mesovortices (as measured by the M3V, ASOS, and citizen weather stations) to the dual Doppler derived flows.