May 26 - July 31
Examining the Relative Motion of Derecho- and Non-Derecho-Producing QLCSs With Respect to the Mean Wind
Matthew Campbell, Ariel Cohen, Andy Dean, Stephen Corfidi, Michael Coniglio, Sarah Corfidi, and Corey Mead
What is already known:
- The classification of mesoscale convective systems (MCSs) relies heavily on inconsistent reporting practices including limited reporting in low-population areas.
- Specific physical features, such as bow echoes and mesoscale convective vortices, have been associated with derecho-producing MCSs but are not an essential part of the current derecho definition.
- There is a positive correlation between MCS speed and damaging-wind potential, with the most intense and long-lived MCSs classified as derechos, but some events are mis-classified.
What this study adds:
- Certain layers of the atmosphere (mean wind in the LCL-EL layer) best represent MCS motion.
- MCS organization/structure can be related to MCS motion, with the best-organized MCSs consisting of a well-defined MCV and transition zone experiencing the fastest motion and propagation and a leading convective line oriented relatively more perpendicular to the mean wind.
- The relationship between MCS structure and MCS motion can be used, in addition to damaging wind reports, to classify MCSs.
Abstract:
Since the term "derecho" was defined, vast technological and societal changes have taken place. Impactful developments include (1) the implementation of the WSR-88D radar network nationwide, which helps provide a structural view of mesoscale convective systems (MCSs), and (2) modern reporting practices which now provide substantially more severe-wind reports than in the past. These changes have caused the term "derecho" to become misapplied over the years, which has led to recent endeavors to refine the definition. This study aims to help clarify the term "derecho" by investigating relationships between radar-implied structural features of MCSs and the mean wind and propagation components of MCS motion. Results show that there is a correlation; specifically, well-organized MCSs move faster and have more propagation in the direction of mean wind than less organized systems. By understanding the relationship between MCS structure and motion, the process of MCS and derecho classification can incorporate physical features and motion of MCSs, in addition to wind-damage swaths, into the classification process.