A few weeks ago, SPC Lead Forecaster Rich Thompson lead a webinar and shared some of the research he has been working on with colleagues at the SPC/NSSL that identifies the convective modes and near-storm environments associated with nearly all tornadoes and significant severe thunderstorm reports from 2003-2011. This topic compliments the ongoing High Shear Low CAPE CSTAR project. Some notes from the presentation are shown below.
There were more than 40 participants in the webinar, with 9 different offices participating including AKQ, CAE, FFC, GSP, LWX, MHX, NCSU, RAH, and RNK. The recorded presentation and the raw power point imagery can be accessed at the links below. If you are outside of the NWS ER LAN, please contact me and I can make the files available to you.
- There was a considerable amount of uncertainty in the mode assignment in this study.
- Between 70-80% of tornadoes in the Carolinas and Virginia are produced by some form of supercell, primarily the discrete and cluster type. This is a similar fraction to tornadoes produced in the Great Plains but the relative rate of occurrence of tornadoes in the Carolinas and Virginia is much less than in the Great Plains.
- Not surprisingly, instability by itself is not necessarily a good discriminator of storm mode. But CAPE is a discriminator between significant supercell tornadoes and QLCS tornado environments, especially in the cool season.
- LCL height is likely a better indicator of strong tornadoes in the Midwest than the eastern U.S. given the typically more moist lower levels in the eastern U.S.
- Effective-layer STP values generally increase with increasing tornado intensity and STP values on the mesoanalysis of 6-8 or more are indicative of a pretty rare environment and pretty strongly associated with high end tornadoes.
- Tornadoes associated with tropical cyclones have the greatest frequency across the Carolinas. Tropical cyclone tornadoes are nearly as frequent as tornadoes not associated with tropical cyclones.
- In the cool season, comparing right moving supercell (F2+) with QLCS (F1+) tornadoes, once the environment gets into the organized convective mode, buoyancy is a better discriminator between supercell versus QLCS tornadoes.
- Shear vector orientations show promise in mode forecasting
Some additional information on the project is available at the following link: http://ams.confex.com/ams/pdfpapers/175726.pdf