Violent Tornado Parameter (VTP)

[Randy Jennings]

This weekend's EF-4 in AL was the first violent (EF-4/5) tornado since the paper on VTP was published. So how did it do? Here is a series of post from author Nick Hampshire's twitter feed:

"Thread: The EF4 Tornado in Alabama was the first violent tornado to occur since our (@cavywx @wxmanted @mattmosier) paper on the Violent Tornado Parameter (VTP) was published. Here is a loop of VTP from the SPC mesoanalysis with tornadoes classified by their rating plotted. (1/?)



VTP is a version of the STP which puts more weight into low level instability, and thus may help forecasters find the mesoscale areas where violent tornadoes are favorable. Attached is STP at the time of the violent tornado. (2/3)



For more information on the VTP you can read the paper here: http://nwafiles.nwas.org/jom/articles/2018/2018-JOM1/2018-JOM1.pdf"

Note: The 1st picture is just a single frame from an animated GIF. I could not figure out how to post an animated GIF. See the source bellow to see the entire animated GIF.

Source: https://twitter.com/nhampshire/status/1102953200238370816

 

[Andy Wehrle]

Looks like it did pretty well, the trick will be reducing the false positives (VTP>STP). In any case, it's clear that composite parameters still aren't the be-all-end-all of severe local storms forecasting.

 

[Quincy Vagell]

I revisited VTP today with a look back at some examples and also read the research more. The 50 cases studied saw an average VTP value of roughly 5 for VTP in violent tornado cases. STP for those same tornadoes was about 3. That should be the base line, so VTP > 5 and especially >3 suggest the environment is not particularly favorable for violent (EF-4+) tornadoes. Whereas STP > 1 suggests the environment is favorable for significant (EF-2+) tornadoes. Just a few things to consider. A VTP of 1 doesn’t say much and it’s very common to see a VTP of 1 where tornadoes, period, are not likely.

Another thing I noticed last year was that VTP skews high across the High Plains, where violent tornadoes are relatively rare. This comes back to steep low-level lapse rates at these elevations in the summer and, often, large low-level buoyancy.

Anyway, here’s a more detailed look at my writeup on VTP, along with four cases over the past year in which VTP threw noteworthy false positives:
https://www.quincyvagell.com/2019/03/21/violent-tornado-parameter/

 

[Rich Thompson]

The calculation displayed on the SPC web page is a simplified version that doesn't (yet) cap the 0-3 km CAPE term, which results in substantially higher values. Once that fix is implemented, you'll see the values drop back to being more consistent with STP, instead of 2-4 x larger in too many cases.