EF4+ Tornado Frequency

[Dan Ross]

First off, this thread isn't about debating the NWS's EF rating for any particular tornado event, but rather to speculate on the actual frequency of tornadoes with EF4+ wind speeds. Most chasers/enthusiasts are probably familiar with the statistic that only 1-2% of tornadoes are EF4 or greater in strength. I often wonder if a larger percentage of tornadoes actually reach that strength. A tornado's intensity can fluctuate throughout its life span. So hypothetically, a tornado that only hits one structure and gets rated EF2 based on that damage alone, might have actually had EF4+ winds at some other point along its path, but we'll never know because it didn't do any surveyable damage. I wonder, if we could somehow accurately (magically) measure the near-surface winds of every tornado, just how many would produce EF4+ wind speeds at some point throughout their life cycle? Might it be 3 - 4%? Maybe more?

 

[Drue Bernardi]

I have no doubt there are tornadoes that achieve that strength but never are rated as such due to lack of damage. How many? Well unless we figure out a way to scan wind speeds at the surface consistently and accurately I doubt we'll ever have any idea. There were several impressive looking and potentially violent tornadoes this year alone that went through sparsely populated areas that could have packed EF4+ winds at some point in their life cycle but were not impacting any structures at the time. That's one of the drawbacks of having a scale reliant on the damage a tornado produces.

 

[Boris Konon]

There is some evidence from Project VORTEX 2 that many tornadoes contain EF2 winds or more sometime during their life spans. I don't know if that means ground level or aloft though.


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[calvinkaskey]

"There is some evidence from Project VORTEX 2 that many tornadoes contain EF2 winds or more sometime during their life spans. I don't know if that means ground level or aloft though."

I've noticed that a lot of tornadoes even in NEw York and the east coast seem to be ef-2, though some seem to be overrated also so I guess it evens out, lol.

 

[Dan Ross]

"There is some evidence from Project VORTEX 2 that many tornadoes contain EF2 winds or more sometime during their life spans. I don't know if that means ground level or aloft though."

I've noticed that a lot of tornadoes even in NEw York and the east coast seem to be ef-2, though some seem to be overrated also so I guess it evens out, lol.

On what grounds do you base your opinion regarding some tornadoes being overrated? I still think that in most events with EF ratings being misrepresentative of the tornado's peak strength, it isn't a case of the NWS overrating based on surveyable damage, but rather underrating due to a lack of surveyable damage and/or verifiable data. But like Drue Bernardi pointed out, there's not much that can be done to resolve the issue without better measuring of near-surface wind speeds. I suppose there's not much more to be discussed here, haha.

 

[Michael Gavan]

Is there data on how many tornadoes received a DEFAULT rating of EF0 because no structure was damaged? If you could somehow just overlay existing percentages to that number it'd be start. Then if we had data on how many EF1 and EF2 (and F1 and F2) tornadoes that only hit non-stick built structures we could tinker with that too. Unfortunately the, especially historic, use of the F rating virtually required a well built, wood framed structure to be obliterated for an F4+ rating. Or at least collapsed outer walls for F3. So even when a tornado hit something, if it was a downtown structure, mobile home, barn, etc it was effectively capped at F2 with a few exceptions. http://www.spc.noaa.gov/faq/tornado/f-scale.html

 

[calvinkaskey]

On what grounds do you base your opinion regarding some tornadoes being overrated? I still think that in most events with EF ratings being misrepresentative of the tornado's peak strength, it isn't a case of the NWS overrating based on surveyable damage, but rather underrating due to a lack of surveyable damage and/or verifiable data. But like Drue Bernardi pointed out, there's not much that can be done to resolve the issue without better measuring of near-surface wind speeds. I suppose there's not much more to be discussed here, haha.

I was only talking about in the East, specifically New York area, sorry I was not more clear.

I'm specifically talking about three tornadoes in New York rated ef-3. I can't see anything I would say looks like ef-3 tree damage. I've looked online, at the pictures on the local NWS sites. The Booneville, New York tornado of 1983

Maybe at :16 seconds left on this video is the ef-3 damage from the Binghamton tornado of May 31, 1998 http://www.wbng.com/news/local/WBNG...y-of-1998---Part-3-WITH-PHOTOS-303688871.html

Damage is seen at 3:02. http://www.weather.gov/bgm/pastSevereMay311998 May 22, 2014 tornado near Albany http://thevane.gawker.com/the-national-weather-service-couldnt-send-out-tornado-w-1580370776 I don't see any ef-3 damage to any trees in any of the videos or pictures or cars and in the video the structures just seems to have collapsed.

 

[Jeff Duda]

Is there data on how many tornadoes received a DEFAULT rating of EF0 because no structure was damaged?

My understanding is that in such cases, the tornado is supposed to be rated EF-unknown, and therefore should not be used in any statistical analysis unless there were other observations of the tornado wind speed (that weren't used in the rating process) that can give some reasonable idea of the tornado wind speeds. Seems we don't see too many EF-U (!) ratings.

 

[Dan Ross]

I was only talking about in the East, specifically New York area, sorry I was not more clear.

I'm specifically talking about three tornadoes in New York rated ef-3. I can't see anything I would say looks like ef-3 tree damage. I've looked online, at the pictures on the local NWS sites.

In the Booneville video, 1:06-1:12 looks like potential EF-3 damage, but then again we have no knowledge of what that building was or of its structural integrity, which leads me to why I'd rather not discuss specific events in this thread: You and I were not there, and cannot know every detail. All we have are some pictures and old video that may or may not cover every structure that was damaged. Also I don't believe you or I know the rating criteria as intimately as those who are professionally trained to survey tornado damage.

On another note, I wonder how much EF-4+ stats would rise if we ignored non-mesocyclone tornadoes, and limited ourselves to only those produced by supercells? I believe the strongest recorded non-mesocyclone tornado was EF-3, and to my knowledge that is quite rare. From a chaser's perspective they certainly have a "watering down" effect on EF-4+ stats, considering that typically when chasers think tornadoes, they're thinking about supercells.