2011-04-27 MISC: AL,TN,MS,KY,OH,IN,WV,GA

[Andy Wehrle]

Let me reiterate: from a synoptic standpoint, there was little about this setup that was unusual, uncommon, or difficult for the atmosphere to achieve.

Spot on. Wasn't it just last October that the most powerful extratropical storm system (on a synoptic scale) in North American history took place? While there was indeed a tornado outbreak in the warm sector of that system, it didn't come anywhere close to the violence of Wednesday's.

 

[Dave Kaplow]

This is what always floors me about major severe weather outbreaks. The same thing was true of the Super Outbreak, and probably of other known major severe weather outbreaks (I only know this fact about the Super Outbreak due to this paper). It's sort of frightening to realize that such a major severe weather event can be spawned from a seemingly innocent looking synoptic setup. Granted, anyone with experience watching synoptic scale patterns associated with major tornado outbreaks would've been able to recognize the potential this day had when looking at model forecasts a few days out. But really, the same ingredients that were in this event are in many severe weather events, even those that aren't major:
-a moderate amplitude trough aloft with neutral to negative tilt that was propagating east/northeast
-moderately unstable air mass with mid-upper 60s dewpoints in the warm sector and 80-90 F surface temperatures
-Strong low-level and deep layer shear
-Moderate low-level instability
-A surface boundary or synoptic scale lift to trigger storms

Think about it, how often do you see these features with other severe weather setups? Almost each one appears regularly. Yes, the degree of deep layer and low-level shear was on the extreme end of the statistical distribution, but I have seen such high levels of shear and helicity associated with instability and forcing that did not result in a major tornado outbreak in other cases. There are likely a few smaller ingredients that came together to make these storms spin like tops and drop violent tornadoes left and right. These are the ingredients that projects like VORTEX2 are trying to discover.

Let me reiterate: from a synoptic standpoint, there was little about this setup that was unusual, uncommon, or difficult for the atmosphere to achieve.

Yeah, I've been trying to wrap my head around this conundrum, too... What was so special about the 27th? What magic ingredient was present that was absent on, say, the 26th? The 26th had off-the-scale parameters too, but it produced mostly ragged HP storms, and yet on the next day with similar ingredients we get supercells about as classic as you can get - scads of them! Why? I've often suspected that we're missing something important concerning supercells and how and why they form. I've seen so many situations out here in CT where the numbers all look great - for example, a couple of days last summer with the supercell composite at 18 or higher - and yet storms stubbornly refuse to rotate. I've also seen gorgeous supercells on the Plains that spin for no discernible reason (e.g. supercell composite = 0). Granted, that particular index and others like it are hardly infallible, I'm just using it to illustrate a point. We may think we know all of the ingredients necessary for a tornadic supercell to form, but there are obviously still some things we are either overlooking or have yet to discover. The SPC and meteorologists in general did an absolutely fantastic job predicting Wednesday's outbreak, that's undeniable... But it's also undeniable that we still have much more to learn about these kind of outbreaks. We can say that a big outbreak is possible or even likely given a particular setup, but the exact conditions that guarantee a historic event like 4/27/11, that's something nobody really knows.

 

[Danny Neal]

Good Lord!!!! I know it is preliminary but wow!

http://www.srh.noaa.gov/images/rtimages/srh/stsd/Apr26-27/PrelimTornadoTracks_Release.jpg

 

[George Tincher]

CNN is now saying the total number of fatalities has reached 316. Depending on your source of information for the Super Outbreak (some cite 315 deaths, others 330), we may have just exceeded that outbreak in the most terrible of all statistics.

Also, the Alabama WX blog is saying that Dr. Tim Coleman was in Pratt City this afternoon and that he saw clear evidence of EF5 tornado damage there.

 

[J Allen]

Dave and Jeff,
My feel on this is it just comes down to balance of those ingredients (quite strong 0-1 and 0-3 shear gave the precipitable water values enough to balance the storms back from a HP mode, when you see the image of the dynamic motion within the tornadoes there is no question that the low-level rotation was up there, the forcing was sufficiently subtle to keep it from getting messy). I was talking to a reporter regarding this yesterday, It just doesn't take as much to bugger up an event as we would wish for. If you look at the number of moderate/high risks issued by the NWS so very many of them don't verify to the extent that the NWS is concerned they might. It might be a blue-sky, it might be a dominant HP mode, it might be an ongoing MCS or linear system which peturbs the environment such that discrete supercells do not form. Seeing the radar loop from this event you got the ideal storm mode with sufficient seperation and things went crazy. The thing is, that any of the NWS high risks could do something like this, and their mission is to balance this risk assessment with the false alarm rate. As I pointed out to the reporter, just because it missed this town, or that location this time around, doesn't mean that the next time such ingredients line up over a given location that that town will be similarly spared.

I wonder whether perhaps the low layer instability is that ingredient for those stubborn storms, such that tilting of the horizontal vorticity/ingestion of rotation is countered by a scale scale outflow or just a general lack. After all we are talking a very finely balanced system here, we have all seen just how little it takes for a supercell to change complexion and stop functioning altogether. With indices, every one is imperfect, and I've yet to see a composite indice that actually impresses me with its performance. Its probably better to consider it from the basic mechanisms needed for supercell development, which are actually suprisingly low even in warm-season storms. Giving the storms too much of one ingredient or the other seems to be one of the major reasons for High risk non-events. With those days which don't look likely this commonly lets the specific indices down, and in general there is so much storm scale modification of the environment based on a host of dynamical reasons that all our indices really provide no more than a guide. A danger of approximating an approximation to the atmosphere so it would seem.

Agree completely on the rating front Jeff. I'm glad to see Greg Stumpf and other senior experts getting involved on the rating front (the 2000-2007 period did not see enough of this due to funding of QRT and hesitance to use it).

 

[Chance Metz]

Just heard Jim Cantore on NBC news say that global warming is behind this outbreak of torandoes. Who here belives that? I don't for one. I never thought I would see over 300 deaths from one day of tornadoes but sometmies you get the perfect storm. It is a natural event not something we caused.

 

[rdale]

An excellent look at the "value" of the QRT by Dr Doswell. Must-read.

http://cadiiitalk.blogspot.com/2011/04/disgraceful-sham-of-program.html

 

[Rich Thompson]

Regarding the storm environment, it was not unprecedented. The tornadoes themselves were not unprecedented. However, the more unique aspect of this event (and 3 April 74) is the *number* of classic, discrete supercells *in* the volatile warm sector. No boundary augmentation of ingredients was necessary on the 27th, and nothing occurred that interfered with initiating discrete storms. In most serious tornado outbreaks similar to this, you get discrete initiation in the warm sector as a result of subtle processes (pre-frontal confluence bands, cloud streets, etc.). That was essentially what we were forecasting to occur as of 13z on 4/27, and unfortunately it occurred that way.

Convective mode and initiation is probably the toughest factor to account for in most outbreak situations. 4/27 was definitely on the upper end of the parameter distribution (STP = 12, which is 90th percentile for F4+ tornadoes), but what was more impressive was having multiple supercells *in* that environment. The prior day (4/26) in NE TX saw earlier than expected storm initiation. It was only about 1-2 hours early, but that meant the northward progress of the warm sector got cut off by the new supercells, farther south than earlier forecasts. Once you get something like that started, it can change the entire complexion of an outbreak, by changing the storm mode, location and timing.

 

[J Allen]

In response to the above this is a direct quote of me from an interview yesterday: "Global warming is a difficult question to answer, and a number of people are looking at this worldwide including myself. We are unable to say conclusively as yet whether storms will become more intense or frequent as such storms are produced by the balance of a number of ingredients. With the latest generation of climate models however, it is quite possible some answers and indications to this question will be available. Currently, the results of the work done suggest that thunderstorms will have the potential to occur more frequently and become more intense (producing larger hail for example). Whether that is realised or not, or we are seeing it currently is something we are unable to say for certain. By the same token, tornadoes are such small scale phenomena that we are likely not going to see the influence of global warming on that scale, however in the long run changes to the balance of ingredients may have an effect in the future. Thats the mistake people commonly make with climate change, attempting to attribute a single event, whereas the truth is all you can attribute is changes in the intensity and perhaps frequency, and even then for small scale events this is somewhat uncertain."

I won't get into the is it real debate as that will lead this waay off topic.

 

[Warren Faidley]

Does anyone happen to know what the highest gate to gate shear was recorded on the 27th.

Thanks.

W.

 

[rdale]

An excellent look at the "value" of the QRT by Dr Doswell. Must-read.

http://cadiiitalk.blogspot.com/2011/04/disgraceful-sham-of-program.html

 

[Elaine Spencer]

If all the preliminary tornado tracks Danny referenced above are verified and were continuous, there may have been TWO "tri-state" tornadoes in this outbreak... the Tuscaloosa/Birmingham tornado (MS-AL-GA) and another that started in MS, passed just north of Decatur AL and ended in TN.

Another very disturbing stat: the mayor of Tuscaloosa now says there are 45 dead, 900+ injured and 400 "unconfirmed missing" in his community. Not just unaccounted for, but MISSING, more than 2 days out.

I realize that communications and transportation are very difficult in the stricken areas and there are probably still people that family, neighbors, responders, etc. just haven't been able to get in touch with yet. Still, to have that many people not heard from at all doesn't sound good to me.

 

[Gabe Garfield]

Does anyone happen to know what the highest gate to gate shear was recorded on the 27th.

Thanks.

W.

As far as I know, the largest delta-V across adjacent gates was just SW of Birmingham: 242 kts.

 

[W. Grant Dade]

Not sure if any of you have seen the High Res Vis from today but I zoomed up to show the tornado paths on my blog. Click on the photos for the full size.

 

[E. Clark]

All I can say is weird things happen with Tornadoes.
One hour or so ago I was reading this AP story that mentioned: "Lonnie Golightly picked through the crumbled planks that had once been his house, looking to salvage some of his belongings. He held up a striped tie.
"I used to have a lot of nice ties," he said softly." Just two lines out of a much larger story page.
http://www.google.com/hostednews/ap...o8Oo0w?docId=6c1d46e8e0da45ceb4cf2a377745a9a2

THEN I go to The Alabama Weather Blog and start sifting through viewer submitted images and see a pic of half a bank statement in a guys hand that was found over 70 miles from Tuscaloosa - with Lonnie GoLightly and his wife's names on it. The hair stood up on the back of my neck.
at http://www.alabamawx.com/