What made the Palm Sunday Outbreak so violent?

[Michael Auker]

Since the fortieth anniversary of this outbreak is coming up, i'll pose this question to the experts on this forum: what made this outbreak so destructive? We get outbreaks with a comparable number of tornadoes every year, what made this outbreak such an overachiever? Almost every tornado was strong to violent, and out of the 38 significant tornadoes in the outbreak, 19 were F-4 and F-5's. These are percentages even the Super Outbreak, which had 30 violent tornadoes out of 95 significant, can't match. The intensity of this outbreak puzzles me; while the shear, helicity, etc. must have been great, 60-65 dewpoints seem marginal for an outbreak of this intensity?

 

[Jeff Snyder]

I think a lot of it is based on the fact that this outbreak occurred decades ago, when (a) the relationship between wind speed / the strength of the tornado and the damage produced, and (B) structures were built to much less stringent standards. I mean, you can watch some of the older tornado programs from TV that mention that winds in a tornado may approach 600 mph... Obviously, as the science progressed, we've realized that this isn't really the case. In addition, it's become increasingly clear in the past decade that the integrity of the structure has a lot to do with the damage produced. Tim Marshall has worked extensively on this matter, though I'm not sure he posts here anymore. He did a very good presentation a couple of years ago that showed that some of the La Plata damage that was preliminarily labeled F4/F5 was actually closer to F1/F2 (these houses were labeled "sliders"). I think that's one of the main reasons why we haven't seen an F5 for the longest time period since tornado records began in 1950; we haven't had an F5 since 5-3-99...

 

[Robert Dewey]

I think a lot of it is based on the fact that this outbreak occurred decades ago, when (a) the relationship between wind speed / the strength of the tornado and the damage produced, and (B) structures were built to much less stringent standards. I mean, you can watch some of the older tornado programs from TV that mention that winds in a tornado may approach 600 mph... Obviously, as the science progressed, we've realized that this isn't really the case. In addition, it's become increasingly clear in the past decade that the integrity of the structure has a lot to do with the damage produced. Tim Marshall has worked extensively on this matter, though I'm not sure he posts here anymore. He did a very good presentation a couple of years ago that showed that some of the La Plata damage that was preliminarily labeled F4/F5 was actually closer to F1/F2 (these houses were labeled "sliders"). I think that's one of the main reasons why we haven't seen an F5 for the longest time period since tornado records began in 1950; we haven't had an F5 since 5-3-99...

Yeah, but alot of the Palm Sunday tornadoes had very long path lengths, not usually found with weaker tornadoes... Though, I am unsure of the manor in which these path lengths were determined. I would be hesitant to discredit most of the tornado strength reports seen in the Palm Sunday Outbreak though...

Anyway, shear was more than impressive... There was a 135knt jet max moving in at 500mb (seen here: http://www.crh.noaa.gov/dtx/palmsunday/Apr...pr12_00_500.jpg ), which is very rare. Td's of 60-65F with SFC temps in the mid to upper 70's, combined with the right temperature profile aloft, could be quite unstable... Perhaps not as unstable as your typical summer setup, but 2000-2500J/KG would be more than sufficient given the very high degree of speed shear, and directional shear.

 

[Jeff Snyder]

Yeah, but alot of the Palm Sunday tornadoes had very long path lengths, not usually found with weaker tornadoes... Though, I am unsure of the manor in which these path lengths were determined. I would be hesitant to discredit most of the tornado strength reports seen in the Palm Sunday Outbreak though...

Agreed, I didn't mean to make it sound like I was saying that there weren't any violent tornadoes on this outbreak by today's standards... I just think that, if it were to happen again today, the numbers of strong/violent tornadoes wouldn't be what they were back then..

Anyway, shear was more than impressive... There was a 135knt jet max moving in at 500mb (seen here: http://www.crh.noaa.gov/dtx/palmsunday/Apr...pr12_00_500.jpg ), which is very rare. Td's of 60-65F with SFC temps in the mid to upper 70's, combined with the right temperature profile aloft, could be quite unstable... Perhaps not as unstable as your typical summer setup, but 2000-2500J/KG would be more than sufficient given the very high degree of speed shear, and directional shear.

Just a comment about your comment that many of the tornadoes that occurred during this outbreak were long-track... I think it's better to think of tornadoes as "long-lasting" by measuring the longevity of a tornado based upon how long it was on the ground, rather than how much land it covered (track length)... Of course, if we're talking about societal impact, then track legnth would obviously be very important. I say this because the time the tornado was the on the ground takes storm motion / tornado forward motion out of the equation, whereas track length is highly dependent upon storm motion... With 135kt 500mb jet streak upstream, I can't help but imagine that many of the tornadoes were moving incredibly quickly, which definately would help the tornado have a long track-length.

 

[Robert Dewey]

Just a comment about your comment that many of the tornadoes that occurred during this outbreak were long-track... I think it's better to think of tornadoes as "long-lasting" by measuring the longevity of a tornado based upon how long it was on the ground, rather than how much land it covered (track length)... Of course, if we're talking about societal impact, then track legnth would obviously be very important. I say this because the time the tornado was the on the ground takes storm motion / tornado forward motion out of the equation, whereas track length is highly dependent upon storm motion... With 135kt 500mb jet streak upstream, I can't help but imagine that many of the tornadoes were moving incredibly quickly, which definately would help the tornado have a long track-length.

Definately...

As far as storm speeds, I would think that they would be in the range of 70-80mph... So that means many of those tornadoes lasted only 30 minutes or so (some up to an hour), though they covered a rather long spatial length. Still, 30 minutes is quite awhile, let alone one hour - So the track length can be deceiving. Definately not chaseable at all, you would have to "intercept" the storm, and even that would be very hard (unlike squall lines, since you have a large area of severe weather, it's relatively easy to put yourself in the line of fire).

DTX:

Detroit Radar showed a rapid increase in thunderstorms over West Central and Southwest Lower Michigan and Northern Indiana by late afternoon. Storm movement was pegged east northeast at around 70 mph! As these storms roared into South-Central Lower Michigan, two horrible twisters were spawned over Branch County, one at East Gilead at 715 PM EST and the other, just a half hour later, southwest of Kinderhook (or, nearly in the same spot as the first).

EDIT: UPDATED TO ADD THIS LINK http://www.crh.noaa.gov/dtx/palmsunday/

THERE IS SOME GOOD INFORMATION ABOUT THE PALM SUNDAY OUTBREAK...

 

[Joe Nield]

I've been doing some work on this in preparation for the upcoming anniversary. In fact, I'll be presenting on the subject at Purdue University and the Russiaville Historical Society over the next month.

While unrelated to the topic of my presentation, I did take some time to think about this very concept. 37 tornadoes, every one deemed significant (F2 or greater, by the Grazulis definition). Now, retroactive ratings played some role, I'm sure, but when you look at some of the damage pictures, you're seeing some with trees mangled and debarked, houses swept off foundations and disintegrated...I'm inclined to believe that it is a combination of retroactive rating problems and I also think it's possible that there were more, and weaker, tornadoes on that day, but in the light of all the destruction perhaps they weren't reported. Public awareness being what it was, it certainly is within the realm of possibility for someone to lose some trees and a few shingles, maybe a barn, and just write it off as storm damage and say to heck with it.

Meteorologically speaking, while I haven't taken a look at the synoptic setup, early season (March-April) setups will tend to be a bit stronger, which could have played a role as well. One could just as easily ask why there weren't more strong to violent tornadoes on 30 May 2004, and believe me, I've thought about that one quite a bit as well.

 

[Michael Auker]

The Palm Sunday Outbreak has held a special interest for me since I read David Wagler's book The Mighty Whirlwind as a child, which then kindled my interest in severe weather. It made the book more interesting that David Wagler was Amish and wrote from the perspective of the Plain People in hard-hit Elkhart and Lagrange county, Indiana. Has anyone else heard of or read this book?

 

[Bob Hartig]

It's a wonderful book, Michael. I read it and reread it this past winter, being fascinated with the Palm Sunday event myself. Wagler served up some excellent reportage. The first edition of The Mighty Whirlwind was published later in 1965, mere months after the outbreak occurred. It deals primarily with the northern Indiana storms in LaPaz, Wyatt, Dunlap, Goshen, and south of Shipshewana in the Shore area.

Particularly fascinating are Wagler's descriptions of phenomena that we've only since recognized and developed terms for, such as multi-vortex structure and satellite tornadoes. You'll encounter some of the common myths of that ere--i.e. 500 mph wind speeds--but you'll also find some of those myths punctured (forget about opening the windows; there's nothing innately safer about hiding in the southwest corner of the basement).

Wagler did his own speculating on how two object sitting close to each other could get tossed in radically different directions. Very interesting to see how he works out the complexity of shifting tornado winds. But best of all is the human element. Forty years later, this book is well worth the read if you can get hold of it.

 

[Rebecca Robinson]

Jeff, you said that we haven't had an F5 since 5-3-99, do you think its because the NWS doesn't want to scare anyone or do you think its because of other issues.

 

[Jeff Snyder]

Jeff, you said that we haven't had an F5 since 5-3-99, do you think its because the NWS doesn't want to scare anyone or do you think its because of other issues.

I don't think there is much of a political or social agenda behind the lack of F5 tornado ratings for the past 6 years, though politics may most definately play into things a bit. I think the advancing understanding between wind speeds, damage potential, and engineering/structural integrity has been the greatest cause for the absence of this most rare of tornado. Or, maybe it's just chance that the tornadoes that otherwise would have created F5 damage just weren't able to inflict that damage upon significant structures. I know there have been several "high-end F4" tornadoes (e.g. Girard, KS, 5-4-03) since that time, however.

 

[Robert Dewey]

I really dislike the F scale for this reason. It's supposed to be purely a damage scale, for which you may estimate winds. The media always plays into the wind aspect more so than the damage aspect. But, I think tornado ratings have been getting too "picky" over the years, and only wanting to reserve that "F5" for the rare tornado of the decade or whatever (my opinions only)...

Personally, in my opinion only, I believe the F scale winds are too low. I don't understand why they don't just put a car in a wind tunnel, and see what speed it takes to lift it 50 feet or so off the ground.... Sure, the broad scale circulation may be weaker, but subvorticies and small scale pressure drops (outside of the main pressure drop), may cause microscale wind speeds to far exceed current thinking.... When DOW measure that 317MPH wind above the SFC in the OKC tornado (1999), that may have been a broad scale wind circulation, but what about the microscale, or a scale that is only 30 or 40 feet in diameter (i.e. subvorticies)?

 

[Michael Auker]

As we all know, since the La Plata tornado, NWS offices have to bring in experts to judge if a tornado was F-4 or F-5. I have wondered how often they just go ahead and rate a tornado F-3 to avoid the hassle a higher rating would bring??? On the side, if the La Plata tornado wasn't F-5, then what tornado is? That tornado completely leveled and blew away well anchored expensive three story homes! However, I do know Tim Marshall helped survey that damage so there must have been a reason to rate it F-4.

 

[Jeff Snyder]

That tornado completely leveled and blew away well anchored expensive three story homes! However, I do know Tim Marshall helped survey that damage so there must have been a reason to rate it F-4.

And that's exactly why they have "experts" who do the damage assessments for violent tornadoes... Tim Marshall made a presentation at the National Severe Weather Workshop last year about the La Plata tornado. He explained that some of the damage that had been previously given prelim ratings of F4 and F5 were actually more like F2! It seems that some of the homes that were "completely leveled" were not anchored well and literally slid right off their foundation; these structures were termed "Sliders". Many of the houses looked very solid and well-built, except for the fact that they were essentially just sitting on their foundations.

I checked the NSWW04 website, though they have removed the talks (they used to be available online). I wish Tim posted on here more often, since it'd be very interesting to hear the specs.

 

[Jeremy Lemanski]

I wonder how many of the F4s on palm sunday would have been rated lower, F3 or even F2, if they would have occured today? The problem i have with all the past sig. tornados, say from 1970 and before, is the rating is based on photos, eye witnesses, etc. No one can say for sure if lets say the Flint tornado was a F5. Yes, it is likely that it was a F5 by the damage it caused, but what if it happen to hit a string of houses that had poor design, material, etc.?


I think that is why we see less F5 ratings now a days then in years past, for the simple fact that many tornados in yester year got a F5 rating when they shouldn't have.

 

[Rebecca Robinson]

You know I wonder based on the knowledge we have today what they would have rated the Tri State Tornado or even Xenia,OH.