What Defines a "Super" Outbreak of Tornadoes?

[CheeselandSkies]

Starting it here so as not to derail the event thread for next week...

I think Super Outbreak is pretty well understood to only refer to the 1974 and 2011 events.

I agree. Palm Sunday 1965 and March 21, 1932 are hot on their heels but not quite in the same league. Are there any other outbreaks known to have a double-digit count of violent (E/F4+) tornadoes?

 

[Kory]

Starting it here so as not to derail the event thread for next week...

Thank you.

 

[warneagle]

Starting it here so as not to derail the event thread for next week...



I agree. Palm Sunday 1965 and March 21, 1932 are hot on their heels but not quite in the same league. Are there any other outbreaks known to have a double-digit count of violent (E/F4+) tornadoes?

March 21-22, 1952. That event produced the first “official” F5 in Byhalia, MS, but it was later downgraded to an F4. There were 11 total F4s in that event.

 

[warneagle]

Honorable mention in terms of violence goes to the May 31, 1985 outbreak (which produced the F5 in Niles, OH and Wheatland, PA), with 9 violent tornadoes.

 

[CheeselandSkies]

Sooooo...extremely violent outbreaks maybe aren't as rare as it seems at first blush (especially in recent years when it seems rare to get more than 1-2 violent tornadoes per year - a function I'm sure of more stringent rating standards but also a general downturn in activity). Still, 4/3/74 and 4/27/11 stand waaaaaaaay out from the rest of the pack.

 

[warneagle]

Yeah obviously you have to account for the changes in rating standards after 2007, as well as the fact that all ratings before 1970 were assigned retroactively (and that some experts, e.g. Grazulis, often dispute those official retroactive ratings), plus the fact that the total numbers of tornadoes per outbreak in the pre-doppler era are almost certainly underestimates because so many tornadoes (especially weak ones) went undetected. Historical meteorology has some complications that a lot of other types of history don't have. Unless someone did a damage survey or took pictures, tornadoes don't really leave a "paper trail" the way that human history does.

 

[Equus]

Ironically, if we are going by number of violent tornadoes, Palm Sunday 1965 eclipses 4/27/11, but 1965 vs 2011 rating standards is very much a viable subject of debate. I think there are historical outbreaks that would probably fill the gap between slightly lesser events and 74/11 since many small tornadoes were certainly missed until recent decades.

 

[warneagle]

Ironically, if we are going by number of violent tornadoes, Palm Sunday 1965 eclipses 4/27/11, but 1965 vs 2011 rating standards is very much a viable subject of debate. I think there are historical outbreaks that would probably fill the gap between slightly lesser events and 74/11 since many small tornadoes were certainly missed until recent decades.

On the other hand, at least one if not both of the Elkhart/Dunlap, IN tornadoes and the Strongsville, OH tornado on Palm Sunday probably could have been rated F5 (I think one of the Elkhart tornadoes was and then it was downgraded).

 

[NorthGaWeather]

All of the events mentioned are good ones to consider. I'll throw in the April 20th, 1920 outbreak. 224 deaths with 6 tornadoes rated F-4.

 

[SilentShadow87]

I've taken a look at 4/3/74 and 4/11/65 under the lens of more modern, EF-scale rating standards, and it's almost amazing how similar they and 4/27/11 all are in terms of intensity. Just based on my non-expert analysis, 4/27/11 actually has the most violent tornadoes overall, but it's very close.

For what it's worth, based on what I could find here are the violent tornadoes in these outbreaks based on Enhanced Fujita scale standards.

Palm Sunday 1965
Midway, IN - EF5
Sunnyside, IN - EF5*
Toledo, OH - EF5
Pittsfield/Strongsville, OH - EF5
Tipton, IA - EF4
Crystal Lake, IL - EF4
Rainbow Lake, IN - EF4
Manitou Beach, MI (1) - EF4**
Kokomo, IN - EF4
Manitou Beach, MI (2) - EF4
Lebanon, IN - EF4
Lima, OH - EF4
Sidney, OH - EF4

Total: 13

*The Sunnyside tornado was borderline, but the intense debris granulation probably would earn it a marginal EF5 rating.
**The first Manitou Beach tornado was probably just below the EF5 threshold, similar to Tuscaloosa.

1974 Super Outbreak
Xenia, OH - EF5
Brandenburg, KY - EF5
Tanner, AL (1) - EF5
Guin, AL - EF5
Daisy Hill, IN - EF4
New Point, IN - EF4
Parker City, IN - EF4
Sayler Park, OH - EF4*
Monticello, IN - EF4
Mannsville, KY - EF4
Frankfort, KY - EF4
Jasper/Cullman, AL - EF4
Tanner, AL (2) - EF4
Broadview, TN - EF4

Total: 14

*The Sayler Park tornado was another which would probably have been rated high-end EF4, but probably not EF5.

Considering how similar the three outbreaks are, it's possible that this is about the upper limit for a tornado outbreak in this climate. It's also possible that there really are freak, once in 500 year events, like the 1974 outbreak was thought to be for a long time, that actually would produce insane numbers of violent tornadoes even under EF scale standards. If so, let's hope there isn't one in any of our lifetimes.

 

[CheeselandSkies]

I agree with you for the most part, although I'm not 100% convinced that even Xenia would be an EF5 under present-day standards. Of the '74 outbreak I'm really only confident of Brandenburg, Guin and Tanner (1).

 

[buckeye05]

The homes in the subdivisions completely wiped out by the Xenia tornado were nailed to their foundations, not bolted. It would be rated EF4 today, despite it's notoriously violent reputation.