Tornado Size/Shape and F-rating. Any coincidence?

[Mikel Shively]

I am just wondering I have been chasing for a few years now here in the Missouri/ Iowa area, and I was wanting to know everyone elses thought on if a Large wedge equals a F3-F5 or if there is no coincidence at all. I have only seen small cone/ rope shaped tornadoes, in which 1 was a F1, the rest were F0.

 

[mikegeukes]

On the Relationship of Tornado Path Length and Width to Intensity
http://www.nssl.noaa.gov/users/brooks/publ...lengthwidth.pdf

Mike

 

[Jeff Wear]

The size and shape of the tornado's visible condensation funnel is not necessarily an indication of the tornado's strength. In other words - a wedge won't always be a strong/violent tornado, and a rope won't always be a weak tornado. Pampa TX (6/8/1995), Mulvane KS (6/12/2004), and Cedar Park TX (5/27/1997) are some examples of strong/violent tornadoes with relatively narrow condensation funnels, and Stratford TX (5/15/2003) is an example of a weak tornado with a wide condensation funnel. The best way to gauge the intensity of a tornado is by watching how fast the funnel and/or debris rotates.

 

[Justin Turcotte]

In general, the larger the tornado, the stronger based on a couple studies including the one linked above. Keep in mind that larger tornadoes will have the ability to hit more structures and therefore will tend to earn an F-rating more in line with the actual intensity. Smaller torandoes are nothing to sneeze at. The rope stage of a tornado can actually be very intense, owing to angular momentum. The old fulling the arms figure skater cliche.

 

[Brian A. Schmidt]

Isn't the Fujita scale variable for any given tornado? I often hear that a particular storm produced an F-3 or F-5, but I would think a tornado starts out at F0 and progresses up the scale and possibly regresses, or varies in strength over time and distance. I guess what I'm trying to ask is if severity of a storm, or the Fujita rating can vary depending on location? If this is the case, then we can't necessairly get the big picture if investigators only base their ratings on the most heavily damaged areas/neighborhoods.

 

[Robert Dewey]

Isn't the Fujita scale variable for any given tornado? I often hear that a particular storm produced an F-3 or F-5, but I would think a tornado starts out at F0 and progresses up the scale and possibly regresses, or varies in strength over time and distance. I guess what I'm trying to ask is if severity of a storm, or the Fujita rating can vary depending on location? If this is the case, then we can't necessairly get the big picture if investigators only base their ratings on the most heavily damaged areas/neighborhoods.

"Depending on location"... I am assuming you mean location as in a wheat field VS. a neighborhood? That certainly does tend to mess with statistics. Tornadoes east of the MS River tend to be rated strong, because there are many more structures to hit... Tornadoes west of the MS Valley will tend to get a lower rating (possibly even F0), as they are more likely to remain in wheat fields.

In actuality though, the tornadoes in the wheat field may be much stronger than the ones that hit the neighborhoods, but given the fact that wheat can only suffer so much damage, rating them any higher than F0 would be a problem.

It would be interesting to see a second "scientific" scale, which would rate a tornadoes size, path length, and possibly a "potential damage" factor, which could be used in case studies. Of course, it would be hard to do that with every tornado, but for the obvious monsters that hit only wheat fields, it would help... And, the general public need not be aware of this scale, as the original Fujita scale confuses them enough,,,

 

[Bob Hartig]

I guess what I'm trying to ask is if severity of a storm, or the Fujita rating can vary depending on location? If this is the case, then we can't necessairly get the big picture if investigators only base their ratings on the most heavily damaged areas/neighborhoods.

From what I've seen, there seem to be two approaches: an overall F-scale rating, and a more detailed F-scale analysis of tornado paths. For an example of what I mean, check out the following link and look at the path of the infamous 1999 Moore tornado. It has an overall designation of F5, but you'll also find a breakdown of damage intensity along the entire path. http://images.google.com/imgres?imgurl=htt...6lr%3D%26sa%3DG

 

[Greg Stumpf]

In this study:

Speheger, D. A., C.A. Doswell III, and G. J. Stumpf, 2002: The tornadoes of 3 May 1999: event verification in central Oklahoma and related issues. Wea. Forecasting, 17, 362-381.

We countoured the F-scale damage for the "Storm A" tornadoes (the OKC-Moore storm), and then looked at the over area as a percent of then entire path area of the different F-scales.

F-scale interval Area (km2)

F0/F1–F5 49.47
F2–F5 31.44
F3–F5 19.18
F4–F5 6.36
F5 0.87

So while this tornado was rated an F5, only about two percent of the total path area received F5 damage.

 

[Andy Wehrle]

The rope stage of a tornado can actually be very intense, owing to angular momentum. The old fulling the arms figure skater cliche.

The Oakfield, WI tornado in 1996 is a good example of one that did not reach peak intensity until during or immediately prior to its rope-out stage. Through the town of Oakfield the tornado was an F4. It was not deemed an F5 until well built houses were found to have been swept away east of Oakfield.

 

[Mikel Shively]

Thank you everyone for the information and links, I have found it very valuable information.

 

[J Holder]

Size and intensity don't always go hand in hand. There are others with better examples but the tornado that bisected Osage County, KS had a very large condensation funnel (1/4 to 1/2 mile) but the damage path was maybe 200 yards or less.

This tornado was rated an F3 based on damage to a farm in it's path but I even doubt that: The house was located in and ahead of a large stand of trees that when airborne pulverized the house, 18 wheeler and farm machinery in the yard. Had the trees not acted as secondary missiles I doubt you'd have seen but F2 or even F1 damage.

Jon Holder

 

[John MacKay]

I can think of two examples

And they are well-known tornadoes.

The Wichita/Andover, KS tornado of 4/26/91 was an F3 when plowing through the southeast edge of Wichita (famous video at McConnell AFB, where the tornado narrowly missed the B-1 bombers stationed there) and then grew to an F5 as it destroyed Andover (where the 2nd most famous video was shot on this event).

The other is the second tornado I've ever seen, the Mulvane tornado last year (6/12/04). It was a rope tornado that did F1 damage until it lifted slightly for a second or two, and then came back down during its dying stage. During that stage, the tornado did high-end F3 damage.

 

[Greg Campbell]

Most of the reading I've done suggests a strong correlation between central pressure drop and windspeed. This makes sense in that the tor's dynamic pipe will remain in equalibrium only when centrifugal forces are high enough to offset the central vacuum. With a strong updraft creating low core pressures, the tornado will naturaly contract, and/or speed up, until it reaches a steady state.

How this relates to funnel/tube size is no doubt a very complex question (Best answered by someone else, someone who actually knows what they're babbling about.) The meso's average rotation speed, radial velocity profile, vertical velocity profile; updraft intensity and area are probably improtant variables. Throw in ground level rotation and a whole bunch of other less obvious characteristics. These are all going to interract to determine the tor's shape and speed.

This fun kid's site suggests that you can have a mile wide F0 wedge. I'm not so sure. It seems that a large tornado will require a fairly healthy parent storm (capable of strong, sustained, suckage) and that it is therefore more likely to be violent.

I'd be happy to have a clear understanding of the basic question: "Why are some tornadoes larger than others?" Anyone?

-Greg

 

[rdale]

"suggests that you can have a mile wide F0 wedge"

What happens if it only travels over open, barren terrain? No damage. No damage = F0 regardless of wind speeds...

 

[Jeff Snyder]

This fun kid's site suggests that you can have a mile wide F0 wedge. I'm not so sure. It seems that a large tornado will require a fairly healthy parent storm (capable of strong, sustained, suckage) and that it is therefore more likely to be violent.

-Greg

Greg,

There have been "wedge" size tornadoes that haven't been particularly strong AS RATED BY the damage produced. RDale is correct in saying that a large tornado that doesn't hit anything cannot be classified very high on the F-scale. For example:

05/15/2003 F2 1 mile wide Wheeler TX
05/29/2004 1817-1915 20 mile long path length, 1 mile wide, F2 (9 WNW Geary - 2.5 N Geary - 9.2 NNW Calumet)
10/04/1998 2137-2208 27 mile long path length, 3/4 mile wide, F2, 2 SE Boley - IXL - Haydenville - 3 SW Nuyaka

From the various years at http://www.srh.noaa.gov/oun/tornadodata/ok/

I'm sure there have been large tornadoes that have been classified only F0-F1 as well. I will agree with you that, by WIND SPEEDS, most of the large tornadoes are probably compared in strength to tornadoes that are rated much stronger, but the F-scale is purely a damage scale, so this is a moot point.