May 22 - July 28
Analysis of MYRORSS Azimuthal Shear Observations of the Morning QLCS Mesovortices of 27 April 2011
Rachael D. Restelle, Anthony W. Lyza, and Matthew D. Flournoy
What is already known:
- Characteristics of the mesocyclones and the tornadoes from the 27 April 2011 supercells
- Environmental and atmospheric processes leading up to 27 April and the morning QLCS
- QLCS mesovortices form and evolve more rapidly than mesocyclones
What this study adds:
- Low-level observations are higher than mid-level observations for all tornadic mesovortices of the 27 April morning QLCS
- Noticeable peaks in azimuthal shear were identified immediately after tornadogenesis for all mesovortices of the 27 April morning QLCS
- Strong tornadoes are associated with higher azimuthal shear values than weak tornadoes
- The 27 April mesocyclones have higher values than the mesovortices
- The most significant difference in azimuthal shear recorded between the mesocyclones’ and mesovortices’ values from the 27 April outbreak is within the mid-level observations
Abstract:
The most devastating day of the 2011 Super Outbreak, 27 April, started with a quasi-linear convective system (QLCS) forming in the early hours of the morning and tracking primarily through the southeastern United States producing multiple weak and strong tornadoes. Little research exists analyzing this first QLCS of the outbreak, and none has analyzed the azimuthal shear of the system during its non-tornadic and tornadic periods. This study aims to fill that research gap by using the Multi-Year Reanalysis of Remotely Sensed Storms (MYRORSS) database to collect 5-minute observations from the Weather Surveillance Radar 1988- Doppler (WSR-88D) network and align them with the radar-detected times of each mesovortex. In this project, the MYRORSS low-level and mid-level azimuthal shear products of the mesovortices embedded within the QLCS are compared to one another and the azimuthal shear values of the supercells. The average time difference between mesovortex initiation and tornadogenesis is also analyzed for all tornadoes produced by the QLCS, regardless of rating, and then compared between weak (EF0 and EF1) and strong tornadoes (EF2 and EF3). From this research, results show the low-level azimuthal shear values are mostly higher than or equal to the mid-level values and, when comparing the supercell azimuthal shear values to those of the QLCS, the supercells’ values are higher overall. It was also discovered that the QLCS’s average time between a mesovortex’s initiation to the formation of its first tornado was found to be about 11.7 minutes, which is less than the mean lead time for all tornadoes warned in advance.