Tornadoes shifting east in the U.S., study finds, putting more people at risk

[John Farley]

This WaPo article may be hard for some to access due to paywall, but I found it interesting, and includes both a summary of the study's findings and quotes from some of its critics. Arguably, the data is more clear-cut on fewer tornadoes on the Plains than it is on more in the South, but I found it an interesting read.

https://www.washingtonpost.com/weather/2024/06/09/tornado-alley-shifts-south-east-plains/?utm_campaign=wp_the7&utm_medium=email&utm_source=newsletter&wpisrc=nl_the7&carta-url=https%3A%2F%2Fs2.washingtonpost.com%2Fcar-ln-tr%2F3df6388%2F6666da7fa4d8857476cf13e8%2F647bb2dfb5f7f52324107913%2F40%2F83%2F6666da7fa4d8857476cf13e8

 

[JamesCaruso]

Thanks John. The first time I tried to access it, it wanted me to sign up before I could view it. But then I tried again and I was able to read it.

Those maps are interesting. They are not clearly labeled, but I believe it represents average tornado days per year. I was surprised even the earlier period is so low - for example, just one tornado day per year in western Kansas, even in the earlier period??

The "critical" quote from Karen Kosiba doesn't really make sense in this context: "Karen Kosiba, a tornado researcher at the Center for Severe Weather Research, said the greater population density in the Southeast compared with that in the Plains exposes it to more damage. That may be part of why twisters in Alabama and Mississippi appear to be on the ground for longer compared with their Plains counterparts." - The analysis is based on tornado days, what does path length or time on the ground have to do with anything? I'm not being critical of her, she's one of the best, but something's not right in how her perspective was used here...

 

[Warren Faidley]

Ask any chaser who has been chasing for over 20 years and they could tell you the same thing. The drought / climatology shift has been moving the dryline further east for years. When I first started chasing tornadoes over 35 years ago, Lubbock was the tornado capital of the world. Now I think you could say the OKC area is King. I'm not sold that Dixie Alley is all that modified. It's proximity to the Gulf might not be as prone to dryline shifting as the Central Plains.

 

[John Farley]

Jim, they used grid boxes, so the small number of tornado days is probably accounted for by the size of the grid boxes they used, of which I don't think the WaPo article stated the size. I believe that besides the number of tornado days in the grid boxes, they also measured the path length of the tornadoes, which is the part of the study Karen was talking about in the quote you mentioned.

 

[JamesCaruso]

When I first started chasing tornadoes over 35 years ago, Lubbock was the tornado capital of the world

Agreed - for many years I spent almost no time chasing in that area, which is a real shame given that the region west of Lubbock has the best terrain and road network anywhere. But I do feel like the last three years have included much more activity out that way, and further into southwest Texas near Midland and into New Mexico. That could just be anecdotal, and even if real may not signal any actual shift “back”.
.

 

[Mike Smith]

Fujita published a paper in 1975 hypothesizing that tornado alley shifted. The new paper is nothing new. You'll find a link to the paper and more below:

There Is Nothing New About the Hypothesis Tornado Alley Has Moved East

After the Birmingham tornado Monday night, we've seen items like this , emphasizing that the South has a serious risk of strong tornadoes a...

www.mikesmithenterprisesblog.com

 

[Matt Zumbrunn]

Thanks John. The first time I tried to access it, it wanted me to sign up before I could view it. But then I tried again and I was able to read it.

Those maps are interesting. They are not clearly labeled, but I believe it represents average tornado days per year. I was surprised even the earlier period is so low - for example, just one tornado day per year in western Kansas, even in the earlier period??

The "critical" quote from Karen Kosiba doesn't really make sense in this context: "Karen Kosiba, a tornado researcher at the Center for Severe Weather Research, said the greater population density in the Southeast compared with that in the Plains exposes it to more damage. That may be part of why twisters in Alabama and Mississippi appear to be on the ground for longer compared with their Plains counterparts." - The analysis is based on tornado days, what does path length or time on the ground have to do with anything? I'm not being critical of her, she's one of the best, but something's not right in how her perspective was used here...

The article also says they studied path length as well and found it was longer further east. I would imagine it's easier to see a path length in trees and personal property vs grasslands, green wheat, etc. That may be why path length seems longer.

 

[Dan Robinson]

A few points:

- The majority of the large outbreaks have always occurred in the South and east of the Mississippi (both Super Outbreaks, Palm Sunday, Enigma, and so on). 8 of the 10 biggest outbreaks in US history were along/east of the Mississippi.

- Most of the big tornado events along and east of the Mississippi River happen with the deep, dynamic systems in early spring/fall when you have something like 80-100kt jet streaks at 500mb and not as much turning in the low levels to slow storms down. A 90-minute tornado in that environment is going to cover 100+ miles by virtue of the storm motions being so fast. In the Plains, the 90-minute tornadoes happen with things like 30kts at 500mb, and usually top out at a 20-mile track when the storm roots, turns right and slows down to a crawl.

- DI density is a big factor. There is much more for tornadoes to hit in the South. Kosiba touched on this in the article. A EF4/5 tornado in the South is much more likely to encounter higher end DIs than in the Great Plains. The greater tree density in the South is such that a tornado is likely to leave some observable damage in virtually its entire track.

 

[Boris Konon]

Agreed - for many years I spent almost no time chasing in that area, which is a real shame given that the region west of Lubbock has the best terrain and road network anywhere. But I do feel like the last three years have included much more activity out that way, and further into southwest Texas near Midland and into New Mexico. That could just be anecdotal, and even if real may not signal any actual shift “back”.
.

One item though, and this is a constant that does not change regardless of the climate, the Plains are the location that is the most favorable for severe thunderstorms and tornadoes in the world b/c of the geography of the area.

First, when you have a high N-S mountain range present with mean westerly flow aloft and flat, rolling plains to the E, you are going to have lee-side troughing, which promotes SE and E low-level winds often below that mean westerly wind flow aloft. This sets up excellent directional shear on many days, even when no strong synoptic forcing is evident (20 kt from the NW at 500 mb, and 20 kt from the SE at the sfc, voila!, 40 kt 0-6 km shear with 180 deg turning)!

Second, the subsidence off the Rockies promotes an EML much of the time, which leads to steep mid-level lapse rates and a capping inversion. The capping inversion allow sfc-based CAPE to build, with often explosive convective development when the inversion is overcome.

As you head farther E to the MS Valley, you lose that lee troughing/directional shear advantage, and the EML starts wane b/c farther W convection overturns the pristine EML and you are geting into a lower elevation, much more humid climate.

Addiaitonaly, the S low-level jet that ramps up around sundown over the Plains due to the uneven cooling of the sloped elevation higher as you go from E to W, which can and does fire tornadic storms very late when storms struggle to form or sustain during the diurnal max. You don't have this feature nearly as prominent outside the Plains. An excellent example of this was the Greensburg event. Find a case in the SEUS or MS Valley where a single supercell produced multiple strong/violent tornadoes and so many (22) after sunset. In fact, all single supercell events that have produced 20 or more tornadoes have been in the Plains.