Discussion of April 27, 2011 Outbreak

[MNTornadoGuy]

Papers from Manda Chasteen, whose PhD project was primarily focused on various meteorological aspects of the 4/27/2011 outbreak, are out now in EOR.

Unfortunately they are behind a paywall.

 

[andyhb]

Pic of the Ringgold/Apison EF4 tornado I've never seen before.

 

[DetectiveWX]

Jason at 3:30 "Good morning; I'm Jason Simpson in the ABC 33/40 weather center. The NWS has issued a tornado warning for Pickens and Lamar until 4:15 AM." (The start of the squall line event.)
James: It's 5:40; a lot of you are waking up to the sirens going off. (The height of the event)

 

[DetectiveWX]

James: "If your boss or principal gets mad, tell them to call me!" ( referencing the major damage throughout the northern 2/3 of the state and no one should bother driving to school/work)

 

[CheeselandSkies]

James Spann did a legendary job with this historic outbreak and well deserves the national recognition it garnered him; but it seems like before and during every severe setup in his DMA since, he feels compelled to spend at least as much time reassuring people that this isn't another 4/27 as he does forecasting and warning for the event in question.

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[DetectiveWX]

9 AM I assume: With severe weather out of here temporarily, we will return to ABC 33/40 at 9 now. (Thus beginning the 5 hour lull before Armageddon)

 

[Fred Gossage]

James Spann did a legendary job with this historic outbreak and well deserves the national recognition it garnered him; but it seems like before and during every severe setup in his DMA since, he feels compelled to spend at least as much time reassuring people that this isn't another 4/27 as he does forecasting and warning for the event in question.

Sent from my Pixel 4a using Tapatalk

That's because, even 11 years later, more than just an isolated few people still ask that question before severe weather threats, especially the ones that sound significant. That day genuinely scarred people here, and it will be that way for a long time, especially now with social media around so that viewers can have direct access to meteorologists to ask questions and hold conversations. I imagine it would've been the same after events such as 1974 had their been more direct ways to communicate then. People were still utterly terrified after that event for many years, but there was no way to quickly communicate those thoughts to people outside of their family and friends.

 

[DetectiveWX]

At this time, MS and AL were 45 minutes to an hour away from Armageddon. E TN was 2-3 hours away while N GA folks were 5.5 hours away.

 

[Fred Gossage]

I tend to think that had the predawn and morning rounds of storms not been there, we probably would've had an event with a similar aerial coverage of violent tornadoes that would've been similar to that of 4/3/1974 or Palm Sunday 1965. In the two days leading up to 4/27, models were consistently showing an environment over middle TN into southern KY that was just as moist an unstable (68+ dewpoints and 3000+ CAPE) as MS/AL, but with surface winds on the large scale backed more straight SE than what was expected in MS/AL. Had the warm sector been clean that far north, I think we would've had a violent tornado environment that would've extended to the Ohio River, and given the spacing of the violent tornadoes in MS/AL as is and how many EF5s we got out of it, I wouldn't be shocked if we would've gotten more EF5 tornadoes from 4/27/11 than from 4/3/74 had TN and KY been working with a warm sector that was clean and not cut off from convection to the south.

 

[DetectiveWX]

Infamous first words
"It's 2PM. I'm James Spann in the weather center. First off, we have a high risk for severe weather; everyone should know by now, and a new Tornado watch (A PDS) is in effect for all of our viewing area until 10PM. A particularly dangerous situation means we could see a few long-tracked, violent tornadoes." (A few was vastly underdone here...) "Lets go to the radar and we see a supercell storm forming near Berry, a town that was devastated by that violent squall line this morning, and we see the tornado impact is a 4.4.
Jason: 12.6. Wow!
Spann: "The Significant tornado index is a 12.6? I thought it stopped at 10. Well we've just learned that, but that just shows you how volatile the atmosphere is today. Let's hold it here for a little bit. In fact, we might be holding it here for 10 hours..."
2:09: We just got a tornado warning for Walker and Winston until 3PM... Thus starting the 8 hours of terror in AL.

 

[Fred Gossage]

An interesting tidbit about that Significant Tornado Index in their radar software from back then... We didn't realize it at the time, but instead of that being WSI's equivalent of the Baron Tornado Index and just a 1-10 ranking, that was just their point-readout of the STP and WSI used the word "Index" instead of "Parameter". It was just a readout of mesoscale analysis data at the location of the SCIT in the radar data, similar to the CAPE, SRH, etc., that was also listed in those marquee boxes when they came up. This explains why the "Significant Tornado Index" was as high as 15-17.5 later in the coverage... because mesoanalysis STP values ended up running that high in west central Alabama that afternoon. The "Tornado Impact" number is their answer to the Baron Tornado Index (BTI) and does run 0-10 or 1-10 like the BTI does.

 

[WxMan42711]

I tend to think that had the predawn and morning rounds of storms not been there, we probably would've had an event with a similar aerial coverage of violent tornadoes that would've been similar to that of 4/3/1974 or Palm Sunday 1965. In the two days leading up to 4/27, models were consistently showing an environment over middle TN into southern KY that was just as moist an unstable (68+ dewpoints and 3000+ CAPE) as MS/AL, but with surface winds on the large scale backed more straight SE than what was expected in MS/AL. Had the warm sector been clean that far north, I think we would've had a violent tornado environment that would've extended to the Ohio River, and given the spacing of the violent tornadoes in MS/AL as is and how many EF5s we got out of it, I wouldn't be shocked if we would've gotten more EF5 tornadoes from 4/27/11 than from 4/3/74 had TN and KY been working with a warm sector that was clean and not cut off from convection to the south.

never once thought about this. if that would have occurred ... whew, i dont even want to imagine how much more devastating it would have been.

 

[CheeselandSkies]

I tend to think that had the predawn and morning rounds of storms not been there, we probably would've had an event with a similar aerial coverage of violent tornadoes that would've been similar to that of 4/3/1974 or Palm Sunday 1965. In the two days leading up to 4/27, models were consistently showing an environment over middle TN into southern KY that was just as moist an unstable (68+ dewpoints and 3000+ CAPE) as MS/AL, but with surface winds on the large scale backed more straight SE than what was expected in MS/AL. Had the warm sector been clean that far north, I think we would've had a violent tornado environment that would've extended to the Ohio River, and given the spacing of the violent tornadoes in MS/AL as is and how many EF5s we got out of it, I wouldn't be shocked if we would've gotten more EF5 tornadoes from 4/27/11 than from 4/3/74 had TN and KY been working with a warm sector that was clean and not cut off from convection to the south.

It certainly does make you wonder, as the potential was there for more favorable thermodynamics up into TN/KY/perhaps far southern IN/OH than there actually turned out to be (hence SPC putting the 15 hatch up there). On the other hand, I've often heard it posited that the morning storms laid down a boundary that locally enhanced the already very high SRH and became a sort of violent tornado "highway" from northeast MS into north-central AL (Cullman, Smithville and Hackleburg). So perhaps it would still have been very rough, but not quite as much of a bloodbath for AL. Impossible to know for sure.

 

[Fred Gossage]

It certainly does make you wonder, as the possibility was there for more favorable thermodynamics up into TN/KY/perhaps far southern IN/OH than there actually turned out to be (hence SPC putting the 15 hatch up there). On the other hand, I've often heard it posited that the morning storms laid down a boundary that locally enhanced the already very high SRH and became a sort of violent tornado "highway" from northeast MS into north-central AL (Cullman, Smithville and Hackleburg). So perhaps it would still have been very rough, but not quite as much of a bloodbath for AL. Impossible to know for sure.

I don't think the supercells would've been as jam-packed in there without that boundary in place, but the Philadelphia MS/Cordova-Rainsville AL and the Tuscaloosa/Birmingham/Shoal Creek supercells prove that they probably still would've been just as violent (including EF5 potential), but maybe more widely spaced across the TN Valley counties.

 

[SouthFLwx]

It’s crazy to think that as bad as 4/27 was, it actually could have been worse had everything been 100% perfect for it.

 

[DetectiveWX]

5:08: Infamous line. "This will be a day that will go down in state history, and all you can do is pray for those people."

 

[DetectiveWX]

Once the skycam returned: GOODNESS! Are you kidding me? That's coming up interstate 359 and Skyland. NOBODY SHOULD BE OUT THERE!

 

[StormStalker]

I still remember seeing ambulance after ambulance coming up U.S. Highway 43 into the Shoals from Phil Campbell and Hackleburg. My urologist was actually one of the first doctors on scene down there to help triage and treat the wounded.

 

[TornadoFan]

I'm curious as to how the atmosphere was able to recover so quickly after the early morning storms moved out of the area.

 

[Equus]

The fascinating thing is despite screaming southerly advection the northern third of the state didn't fully recover by the time storms began exploding (the middle third only worked over from the first round before sunrise and the southern third not affected at all, clearing up fast) leaving a subtle WSW to ENE thermal boundary that actually enhanced low level backing and made the situation even worse - truly a day with an amazing environment that'll be discussed for decades to come