An Analysis of Environmental Factors and Radar Features Present Prior to Tornadogenesis in Quasi-Linear Convective Systems

open_access
Open Access
Author:
Melanson, Sean
Area of Honors:
Meteorology and Atmospheric Science
Degree:
Bachelor of Science
Document Type:
Thesis
Thesis Supervisors:
Yvette Pamela Richardson, Thesis Supervisor
Paul Markowski, Thesis Honors Advisor
Keywords:
Thunderstorm
Severe Convection
QLCS
Tornado
Simulation
Abstract:
Quasi-Linear Convective Systems (QLCSs) often produce weak, short-lived tornadoes compared to supercells, but can still produce devastating impacts to the most vulnerable communities, living in poorly constructed houses and mobile homes. QLCS tornadoes are also more challenging to forecast than supercell tornadoes, partly as a result of the lack of radar precursors, resulting in many missed events and false alarms. QLCSs have not garnered as much focus in recent literature as supercells, and as such, progress in QLCS tornado forecasting has been slow. In chapter one of this three-part study, we focus on understanding the challenges associated with predicting QLCS tornadoes by evaluating the effectiveness of existing forecasting tools such as the “Three Ingredients Method'' (3IM) and radar features referred to as “Confidence Builders and Nudgers” (CB/N). We found 3IM to be an effective distinguisher between QLCSs that are likely and unlikely to produce tornadoes but did not find CB/N to add value in determining when and where a forecaster should issue a tornado warning. In chapter two, we apply the K_DP/Z_DR separation method, known as a precursor to tornadogenesis in supercells, to a dataset of tornadic QLCSs using a Python algorithm to determine if it also has merit as a precursor to QLCS tornadogenesis. We found the mean K_DP/Z_DR separation distance to be 20.8 km with a standard deviation of 16.0 km. While a focus on null cases is required in future work to add validity to our findings, our results indicate it may have some value as a forecasting tool. In chapter three, we examined the sensitivity of vertical vorticity and velocity patterns at the leading edge of a QLCS to a heterogeneous shear environment. We performed 4 QLCS simulations, one of which was performed in shear varying sinusoidally in the meridional direction, while the other 3 were run in homogeneous shear of 10, 15, and 20 m/s. We found the QLCS simulated in the homogenous, high-shear domain produced the weakest updrafts and vertical vorticity. In the heterogeneous shear case, our strongest cyclonic vortices were located in weak to moderate shear while the strongest updrafts were located in moderate shear. We hope the results presented in this paper not only provide value to forecasters but stimulate further research on developing new QLCS forecasting tools.