An Environmental Climatology of Quasi-Linear Convective System Mesovortices around Northern Illinois

Mesovortices are vertical vortexes of air that can produce significant severe weather hazards, including tornadoes. Mesovortices can exist along the leading edge of quasi-linear convective systems (QLCS), or linear assemblages of storms. Developing an environmental climatology that assesses environments conducive for QLCS mesovortices across northern Illinois can aid forecaster situational awareness at the National Weather Service (NWS) Chicago, IL and surrounding offices during QLCS severe weather events. Historical WSR-88D radar images of fifty-two QLCSs that impacted the NWS Chicago county warning area and near vicinity were subjectively analyzed to determine the number of mesovortex occurrences. QLCS events were categorized (minor or significant “potential”) based upon the number of mesovortices analyzed. Using archived Rapid Refresh (RAP) and Rapid Update Cycle (RUC) model data, thermodynamic and shear parameters of QLCS environments were evaluated. Additionally, environments were temporally categorized from time of QLCS “impact” (within twenty-five nautical miles of sounding site) as well as one and two hours prior. Thermodynamic parameters of these environments, including surface-based, mean layer, and most unstable convective available potential energies (CAPE), surface inhibitions (CINH), and lifted condensation levels (LCL) showed poor ability at distinguishing between environments favorable for QLCS mesovortices versus those that were not. Shear parameters were of greater utility, at all times, in distinguishing between QLCS “potential” environments. In particular, shear magnitudes from the surface through eight kilometers seem to show the greatest utility at distinguishing QLCS mesovortex potential across northern Illinois. The results point toward the use of shear parameters as a useful mesoanalysis tool in assessing QLCS environments across the region. Similar results have also been observed with prior QLCS mesovortex studies focused on a larger domain of the United States.