Tornado "Death" Alley

[HarlequinBoy]

I found this information on another board I stumbled across today, but thought the finding was very interesting. And in light of Super Tuesday not at all surprising.

An area just to the east of Tornado Alley, commonly called Dixie Alley, has a much higher fatality rate than the rest of the US.

Note the bullsyes over east Arkansas, se Missouri, west and middle Tennessee, north Mississippi and north Alabama. Areas in dark shading includ Little Rock, Memphis, Jackson, Nashville, Birmingham, and Huntsville.


http://www.niu.edu/PubAffairs/RELEASES/ ... nado.shtml


My personal opinion is that nighttime tornadoes play a huge role in this area. Also the majority of tornadoes in the South seem to come from outbreaks..

[wbug1]

Maybe the quality of the home construction is poorer in that area?

Just a thought. Not based on any evidence.

[Squarethecircle]

If it's anything, I bet it's population density.

[Brent]

It's a combination of both

[MGC]

It is a combination of wealth, population density and time of day that the tornado usually hits at, night. Plus most tornados in Dixie Alley are rain wrapped.......MGC

[RL3AO]

Population density is a big part. You can see an increase over the Twin Cities and Tampa where it is more populated.

[HarlequinBoy]

Well with the exception of the Memphis metro, east Arkansas, north Mississippi, and west Tennessee aren't densely populated at all. Neither is southern Missouri.

Population density per square mile
Tennessee 138
Alabama 88
Missouri 81
Texas 80
Mississippi 61
Arkansas 51
Oklahoma 50
Kansas 33

Looking at that, MS and AR aren't significantly higher than Oklahoma. Also there's not an increase in fatality frequency in densely populated areas of Texas like Dallas and Austin.

I think MGC hit it right on the head. It's just a combination of factors, unfortunately.

[RL3AO]

[AnnularCane]

Is there any particular reason they tend to hit at night in this area? I always thought it was a matter of timing.

[HarlequinBoy]

Eastern parts of Tornado Alley and Dixie Alley have similar densities...

[Squarethecircle]

If you look, there are some spikes in Eastern Tornado Alley.

[Ed Mahmoud]

Is there any particular reason they tend to hit at night in this area? I always thought it was a matter of timing.

Just a guess, may have to do with the fact that they are earlier season storms, and driven more by wind dynamics than instability (higher shear/lower CAPE), and the nocturnal jet above the surface that forms. I don't know much about the nocturnal low level jet, it may be partly related to decoupling of the boundary layer. I think it is also related to differential cooling between the Plains and mountains, and points further East.


Maybe an interweb seach on the World Wide Internet will reveal the answer...

[Ed Mahmoud]

Is there any particular reason they tend to hit at night in this area? I always thought it was a matter of timing.

Just a guess, may have to do with the fact that they are earlier season storms, and driven more by wind dynamics than instability (higher shear/lower CAPE), and the nocturnal jet above the surface that forms. I don't know much about the nocturnal low level jet, it may be partly related to decoupling of the boundary layer. I think it is also related to differential cooling between the Plains and mountains, and points further East.


Maybe an interweb seach on the World Wide Internet will reveal the answer...

nocturnal jet
Night-time layer of strong wind, of supergeostrophic speed, at a height of a few hundred metres above ground. Such a layer may develop when the strong cooling over land at night separates the flow aloft from the constraint of surface friction.

[wxmann_91]

Is there any particular reason they tend to hit at night in this area? I always thought it was a matter of timing.

Just a guess, may have to do with the fact that they are earlier season storms, and driven more by wind dynamics than instability (higher shear/lower CAPE), and the nocturnal jet above the surface that forms. I don't know much about the nocturnal low level jet, it may be partly related to decoupling of the boundary layer. I think it is also related to differential cooling between the Plains and mountains, and points further East.


Maybe an interweb seach on the World Wide Internet will reveal the answer...

yep, that would be correct. The nocturnal LLJ helps to fuel nocturnal tornadoes. Also these cool-season events occur when the days are shorter. There are actually two peaks during the day when SE tornadoes are most prevalent: the traditional one around dusk and a far scarier one in the wee hours of the morning (perfectly evidenced by the AL tornadoes during the Super Tuesday outbreak). The population in the S is scattered and that may play a role too; those living in relatively isolated communities and/or mobile home parks may not know what's coming until it's too late if they don't have an NWR or TV (contrasting with bigger towns which may have tornado sirens). Then, of course, the concentration of mobile homes is much bigger in the SE and they are deathtraps in tornadoes. Also winter is often not a time when one thinks of tornadoes, lack of public awareness may play a factor.

[yzerfan]

I spent a couple of years living in west Tennessee, and I was surprised at how extremely poor the building codes there seemed to be- not just fro ma weather standpoint, but from the people we talked to, there was pretty much zero concern about earthquakes from the New Madrid as well.

[Ptarmigan]

I think there are various reasons why many people die in tornadoes in East Arkansas, Southeast Missouri, West and Central Tennessee, North Mississippi and Alabama are the following:
-Tornadoes form at night, which makes them harder to see. Also, tornadoes form when people are asleep and are less lilely to hear alarms.
-Tornadoes are harder to see because they are in rain wrapped storms.
-People living the area think that large and deadly tornadoes happen in Tornado Alley.
-Building codes are not up to standards for tornadoes.
-Tornado season for that area occur in winter and people think tornadoes only happen in warmer times of spring and summer. Tornadoes can happen any time of the year.
-Higher population density than in tornado Alley.

Here is a map of tornado activity per square mile.


Tornado Risk Map

[Ed Mahmoud]

I think there are various reasons why many people die in tornadoes in East Arkansas, Southeast Missouri, West and Central Tennessee, North Mississippi and Alabama are the following:
-Tornadoes form at night, which makes them harder to see. Also, tornadoes form when people are asleep and are less lilely to hear alarms.
-Tornadoes are harder to see because they are in rain wrapped storms.
-People living the area think that large and deadly tornadoes happen in Tornado Alley.
-Building codes are not up to standards for tornadoes.
-Tornado season for that area occur in winter and people think tornadoes only happen in warmer times of spring and summer. Tornadoes can happen any time of the year.
-Higher population density than in tornado Alley.

Here is a map of tornado activity per square mile.


Tornado Risk Map

The tornado frequency map is obviously biased to where people live. I somehow doubt the DFW Metroplex and Oklahoma City have more tornadoes than the more lightly populated areas in between on I-35, for example. And somehow I suspect one little area of SW Massachusetts having a Highest Risk when the Texas Panhandle doesn't is also a function of population density.

[simplykristi]

I agree with what MGC posted.

Kristi

[HurricaneBill]

Another thing to remember:

In Tornado Alley, land is pretty much flat, so you can see a tornado coming from miles away. However, in the Tornado "Death" Alley, there are hills and forests that likely obscure tornadoes.