Discussion (May 18-19-20-21) Moore Tornado EF-5 from NWS

[JonathanBelles]

Personally, what I would look for in an EF-5 would be a symbiosis of ground and atmosphere. By that I mean that I would be looking for more than a complete sweep of the ground. I would be looking for ground and cement to be moved and removed, or signs of tremendous impact of two objects i.e. a playing card being cut into trees or a 2X4 being shoved into cement. I would not take the rating lightly, but I have no ground experience in ratings.

[brunota2003]

Personally, what I would look for in an EF-5 would be a symbiosis of ground and atmosphere. By that I mean that I would be looking for more than a complete sweep of the ground. I would be looking for ground and cement to be moved and removed, or signs of tremendous impact of two objects i.e. a playing card being cut into trees or a 2X4 being shoved into cement. I would not take the rating lightly, but I have no ground experience in ratings.

Well, what I posted were things from the SPC page (regarding damage indicators). I did not post every little thing that had some part of the upper bounds at >200 mph, just things that were close for expected, and had a good degree of the bounds above 200 mph. I don't think there is anything with both lower and upper bounds at 200+, but you can get a pretty good idea of just what kind of devastation they'd be looking for, regarding EF-5.

http://www.spc.noaa.gov/efscale/ef-scale.html

There is a list of the different damage indicators, and if you click on them, they give a description of the item, the degree of damage, and what the expected, lower and upper limits are for the winds!

[Ntxw]

Lets not forget construction quality is often the important factor in differentiating EF4 from EF5. If an EF5 swings by a mobile home park all we would see from it is high end Ef3 to EF4 even if all the homes there were destroyed.

[brunota2003]

Reports of ground scoured at that mobile home park:

http://abcnews.go.com/US/wireStory/tornadoes-hit-kan-okla-injuries-reported-19213075#.UZmRFCvwLGs

Not sure how accurate that report is, but that is often a signal of EF-5 damage. However, I agree with the others that the pictures I saw did not support EF-5 damage. We will find out eventually though.

It is very possible, though I think I've heard of the ground being scoured in EF-4s before? I don't remember, and there is no "damage indicator" for the ground, unfortunately. I wish they had one for vehicles, if a vehicle is lobbed "x" feet, it would generally be "x" mph winds, none for those, either though.

[brunota2003]

@NWSWichita: Damage survey revealed EF1 tornado southwest of Wichita with a 4.6 mile path length and 0.5 mile width. #kswx

[CrazyC83]

It think it was violent it could have been a EF-5. Although I know they are very careful about giving out that rating.

Well, to give EF-5, you need to see:

1. Multiple houses completely leveled, with the concrete slab completely wiped clean (the reason I say multiple is that one or two houses could be within EF-4 damage, but if many houses are like that, then it increases the likelihood of >200 mph winds)

2. The complete destruction of an institutional building (ie, hospital, courthouse, state or federal building, etc), or

3. Significant/permanent structural deformation of a high/mid rise building (respectively).

While the damage is bad, right now from what I have seen, it supports upper EF-3 or lower EF-4.

(Note: This list is not all inclusive, just some examples of what you need to get an EF-5 rating)

The recent EF-5 rating bases:

Greensburg, KS 2007 - Multiple institutional buildings flattened

Parkersburg, IA 2008 - Well-built single family homes blown away

Philadelphia, MS 2011 - Deep ground scouring amidst flattened houses (the ground movements caused the upgrade since the houses were only EF-4)

Smithville, MS 2011 - Multiple types of buildings blown away

Hackleburg/Phil Campbell, AL 2011 - Multiple types of buildings blown away

Rainsville, AL 2011 - Ground scouring and well-built houses blown away

Joplin, MS 2011 - Overall devastation, with Mercy Hospital the big determinant

Piedmont, OK 2011 - Surface observation of 279 mph wind gust elevated translating to about 220 mph at surface (house damage was leaning EF-4)

[brunota2003]

Lets not forget construction quality is often the important factor in differentiating EF4 from EF5. If an EF5 swings by a mobile home park all we would see from it is high end Ef3 to EF4 even if all the homes there were destroyed.

I agree, but in this case even away from the park, with regular houses, still only seeing upper EF-3, with maybe isolated EF-4 in spots. We'll see what else the survey teams see in the morning, that we may not have yet, and what they rate it.

Regardless though, my thoughts and prayers go out to those impacted.

[EF-5bigj]

It may or may not have been a EF-5. Then again where I live in Dixie Alley violent tornadoes happen pretty often I have seen. So maybe that's why I expect tornados to be stronger.

[SouthDadeFish]

Reports of ground scoured at that mobile home park:

http://abcnews.go.com/US/wireStory/tornadoes-hit-kan-okla-injuries-reported-19213075#.UZmRFCvwLGs

Not sure how accurate that report is, but that is often a signal of EF-5 damage. However, I agree with the others that the pictures I saw did not support EF-5 damage. We will find out eventually though.

It is very possible, though I think I've heard of the ground being scoured in EF-4s before? I don't remember, and there is no "damage indicator" for the ground, unfortunately. I wish they had one for vehicles, if a vehicle is lobbed "x" feet, it would generally be "x" mph winds, none for those, either though.

The other day, I stumbled across a PDF by the NWS (I believe) showing what surveyors use to distinguish between EF 4 and EF 5 damage. Ground scouring was an indicator they used for some EF 5 cases. If I find the PowerPoint again I will post it here. Also about your vehicle comment, they made remarks showing that in EF 5 conditions vehicles are often found severely twisted around objects such as trees.

EDIT: just found the aforementioned PDF

http://www.norman.noaa.gov/nsww/wp-content/uploads/2012/03/LaDue_NSWW2012.pdf

[brunota2003]

The other day, I stumbled across a PowerPoint by the NWS (I believe) showing what surveyors use to distinguish between EF 4 and EF 5 damage. Ground scouring was an indicator they used for some EF 5 cases. If I find the PowerPoint again I will post it here. Also about your vehicle comment, they made remarks showing that in EF 5 conditions vehicles are often found severely twisted around objects such as trees.

Very interesting info there (along with your list, Crazy)! Something I'll have to keep in mind. Some cases for EF-5 are clearly obvious, others are right on the verge, so that article will be an interesting read!

[SouthDadeFish]

Sorry, it was a PDF not a PPT. I got confused. Nonetheless, I hope it helps everyone!

[EF-5bigj]

EF-4 to EF-5 ratings can be pretty close damage wise. As both just cause utter devastation

[CrazyC83]

EF-4 to EF-5 ratings can be pretty close damage wise. As both just cause utter devastation

That is very true, often an extra influence (i.e. ground scouring) is required.

[cycloneye]

The dividing of threads for this event has been very positive as we are getting healthy discussions that may have been lost with the posting of watches and warnings. Those members who may not have the full knowledge about the many aspects of severe weather are learning from this discussion so let's keep it going. And definitely,this format of divided threads has come to stay.

[Bunkertor]

Reports of ground scoured at that mobile home park:

http://abcnews.go.com/US/wireStory/tornadoes-hit-kan-okla-injuries-reported-19213075#.UZmRFCvwLGs

Not sure how accurate that report is, but that is often a signal of EF-5 damage. However, I agree with the others that the pictures I saw did not support EF-5 damage. We will find out eventually though.

Hm, what pressure would be required to rip grass off the soil ?

[CrazyC83]

If grass was pulled off, that is a good indicator of at least an EF-4. I'd want to see the ground ripped out for a 5 though.

[EF-5bigj]

So scouring is usually a sign of a violent tornado? I'm learning new tornado facts on this thread already prayers for those affected by that violent tornado though.

[Ntxw]

So scouring is usually a sign of a violent tornado? I'm learning new tornado facts on this thread already prayers for those affected by that violent tornado though.

Probably not alone. But it is one side evidence that builds confidence when added to complete destruction of well built structures. It seems we shouldn't look for something specific but additional pieces (debarked trees, thick nails stripped etc) to build a scene of violent winds.

[WeatherGuesser]

Thoughts on Moderate for Tuesday (which would be four days in a row)?

[TwisterFanatic]

Monday looks to be another dangerous day. Not line of storms going through OK tonight that can take some energy out of the atmosphere, which is what people were hoping for. Will be recharged big time tomorrow afternoon/evening.