April 26-28, 2011 "Dixie Alley Tornado Outbreak"...Greatest in history?

[Bobby Prentice]

The April 26-28, 2011 "Dixie Alley Tornado Outbreak" is a contender for the largest tornado outbreak in U.S. history, perhaps even greater than the "Super Outbreak" of April 3-4, 1974 in some aspects. That outbreak resulted in 6 F5s, 24 F4s, 34 F3s, 34 F2, 33 F1s, and 19 F0s for a total of 148 tornadoes.

OUTBREAK...The term outbreak is used when referring to a group or family of six or more torndoes which are spawned by the same general weather system. Six tornadoes from two different thunderstorms cells, in advance of a cold front might be called a small outbreak. Six scattered tornadoes from different weather systems in three states should not be called an outbreak. This definition is from Galway (1977). Later that year, (personal conversation) he defined an outbreak of 10 ore more tornadoes from a single organized weather system. This book uses the six-tornado definition. The author has added the following addition to that definition: The end of one outbreak and the start of another is marked by a greater than six-hour lull in tornado activity, and an outbreak need not be confined to a single calendar day. Thus, if tornado activity subsides at 2 AM, and begins again at 2 PM, the Project considered that new activity to be the start of a different outbreak.

Based on the Grazulis definition and the SPC Storm Reports (rough log), the April 26-28 outbreak actually began with this report:

2156 1 E MABANK KAUFMAN TX3237 9608 TORNADO REPORTED ON GROUND NEAR MABANK. (FWD)

and ended 47 hours and 40 minutes later with this report:

2136 KNOTTS ISLAND CURRITUCK NC3651 7592 TORNADO ON GROUND REPORTED BY PUBLIC (AKQ)

As of May 3, 2011, the total SPC Storm Reports (rough log) tornado count for this outbreak was 388 broken up like this:

April 26, 2011.....107 (four early tornadoes in the log were not counted due to time/space constraints)
April 27, 2011.....268
April 28, 2011.......14
GRAND TOTAL=389

I know that the SPC Storm Reports (rough log) over-counts tornadoes even more since the filtering criteria standards were recently relaxed. However, even if only 40% of these reports verify, it would exceed the Super Outbreak of 1974. There is already support from NOAA for a big count:

NOAA April 2011 Tornado Information - April 26-28, 2011, Tornado Outbreak Statistics

As of May 3, NOAA's preliminary estimate is that there were 305 tornadoes during the entire outbreak from 8:00 a.m. EDT April 26 to 8:00 a.m. April 28, 2011.

Funny part is, the April 14-16, 2011 tornado sequence already has 155 confirmed tornadoes (according to Wikipedia) and might have beaten the Super Outbreak total (according to the Grazulis definition), but there was a 6 hour and 39 minute break between tornadoes on the morning of April 16 (between 1002Z and 1641Z).

Here's what the the outbreak looks like on the individual SPC Storm Reports maps:





Here is the preliminary tornado survey information for the outbreak from NWS Southern Region area of responsibility (NOTE: This does not include April 26 tornadoes over TX/LA/AR, April 28 tornadoes over the Carolina's and it does not include paths over NWS Central or Eastern Regions):

Tornado totals (142 of them) over NWS Southern Region (only) as of Tuesday, May 3:
[FONT=&quot]EF-5: 2[/FONT]
[FONT=&quot]EF-4: 12[/FONT]
[FONT=&quot]EF-3: 20[/FONT]
[FONT=&quot]EF-2: 39[/FONT]
[FONT=&quot]EF-1: 40[/FONT]
[FONT=&quot]EF-0: 29[/FONT]

Curios tidbits:
Max path width greater than or equal to one (1) mile...5
Max path width greater than or equal to one-half (0.5) miles...25

How does this outbreak rank? Grazulis's work provides some historical perspective, at least through 1995:

Outbreaks with 20 or more Significant (F2-F5) Tornadoes, 1880-1995

...Date.........significant....F4/F5.......killer
.................tornadoes...tornadoes...tornadoes
Apr 03-04, 1974 ... 95 ........ 30 ........ 49 (Super)
Nov 21-23, 1992 ... 42 ......... 5 ......... 9
Apr 11-12, 1965 ... 38 ........ 19 ........ 21 (Palm Sunday 1965)
Feb 19-20, 1884 ... 37 ......... 4 ........ 28 (Enigma)
Mar 21-22, 1932 ... 36 ........ 10 ........ 27 (Deep South)
Apr 29-30, 1909 ... 35 ......... 4 ........ 24
Jun 05-06, 1916 ... 34 ......... 1 ........ 23
Apr 15-16, 1921 ... 34 ......... 1 ........ 17
May 08-09, 1927 ... 32 ......... 8 ........ 17
Mar .. 28, 1920 ... 31 ......... 8 ........ 19 (Palm Sunday 1920)
Mar 30-31, 1933 ... 30 ......... 1 ........ 16
May .. 20, 1949 ... 29 ......... 2 ......... 5
Apr 23-24, 1909 ... 29 ......... 6 ........ 16
Apr 10-11, 1979 ... 28 ......... 2 ......... 5 (Red River Valley)
Mar .. 25, 1884 ... 27 ......... 0 ........ 12
Jun 02-03, 1990 ... 27 ......... 7 ......... 4 (Lower Ohio Valley)
Mar 30-31, 1938 ... 26 ......... 3 ......... 9
Jun 07-08, 1984 ... 26 ......... 2 ......... 4 (Barneveld, WI)
Mar .. 13, 1990 ... 26 ......... 4 ......... 2
Apr 26-27, 1991 ... 26 ......... 5 ......... 5 (Andover, KS)
May 26-29, 1973 ... 26 ......... 3 ......... 8
Mar .. 16, 1942 ... 25 ......... 7 ........ 18
Mar .. 19, 1948 ... 25 ......... 3 ......... 5 (Alton-Bunker Hill-Gillespie)
May .. 05, 1960 ... 25 ......... 4 ......... 8
Mar .. 27, 1890 ... 24 ......... 6 ........ 16 (Mid Mississippi Valley)
Apr .. 30, 1924 ... 24 ......... 2 ........ 16
Apr .. 02, 1982 ... 24 ......... 4 ........ 10
Apr 15-17, 1939 ... 23 ......... 2 ........ 10
Apr .. 18, 1880 ... 22 ......... 5 ........ 14
May .. 05, 1930 ... 22 ......... 5 ......... 4
Feb 05-06, 1942 ... 22 ......... 0 ......... 9
May .. 18, 1883 ... 21 ......... 6 ........ 16
Nov .. 25, 1926 ... 21 ......... 2 ........ 14
May .. 15, 1943 ... 21 ......... 4 ......... 2
Apr .. 30, 1954 ... 21 ......... 1 ......... 2
Apr 07-08, 1980 ... 21 ......... 0 ......... 1
Mar 13-14, 1913 ... 20 ......... 3 ......... 6
May 27-28, 1917 ... 20 ......... 4 ........ 16
Apr .. 21, 1967 ... 20 ......... 4 ......... 3 (Belvidere-Oak Lawn)
May 15-16, 1968 ... 20 ......... 4 ......... 8
May .. 31, 1985 ... 20 ......... 8 ........ 10

Outbreaks with 40 or more Recorded Tornadoes, 1880-1995

...Date............total....significant....F4/F5.......killer.....total
.................tornadoes...tornadoes...tornadoes...tornadoes...deaths
Apr 03-04, 1974 ... 148 ....... 95 ........ 30 ........ 48 ...... 315
Sep 19-23, 1967 ... 111 ....... 15 ......... 0 ......... 2 ........ 5
May 26-29, 1973 .... 99 ....... 26 ......... 3 ......... 8 ....... 22
Nov 21-23, 1992 .... 95 ....... 43 ......... 5 ......... 9 ....... 26
May 18-19, 1995 .... 80 ....... 17 ......... 2 ......... 2 ........ 4
May 11-12, 1982 .... 70 ....... 13 ......... 1 ......... 1 ........ 2
Apr 26-27, 1994 .... 67 ........ 9 ......... 1 ......... 1 ........ 3
Mar 20-21, 1976 .... 66 ....... 18 ......... 3 ......... 3 ........ 3
Jun 02-03, 1990 .... 66 ....... 27 ......... 7.......... 4 ........ 9
Jun .. 16, 1992 .... 65 ....... 12 ......... 2 ......... 1 ........ 1
Jun 26-27, 1992 .... 62 ....... 11 ......... 0 ......... 2 ........ 2
May 02-03, 1984 .... 60 ....... 15 ......... 1 ......... 1 ........ 5
Mar .. 13, 1990 .... 59 ....... 26 ......... 4 ......... 2 ........ 2
Jun 15-16, 1992 .... 58 ....... 15 ......... 2 ......... 0 ........ 0
Jun .. 08, 1993 .... 58 ........ 2 ......... 0 ......... 0 ........ 0
May .. 08, 1988 .... 57 ........ 8 ......... 0 ......... 0 ........ 0
Apr 26-27, 1991 .... 53 ....... 26 ......... 5 ......... 5 ....... 21
May 25-26, 1965 .... 51 ........ 4 ......... 0 ......... 0 ........ 0
May 04-05, 1959 .... 49 ........ 8 ......... 0 ......... 0 ........ 0
Apr 11-12, 1965 .... 48 ....... 38 ........ 19 ........ 21 ...... 256
Apr 02-03, 1982 .... 48 ....... 24 ......... 4 ........ 10 ....... 29
May 18-20, 1983 .... 48 ....... 10 ......... 0 ......... 6 ........ 6
Jan 09-10, 1975 .... 47 ........ 9 ......... 1 ......... 3 ....... 11
May 15-16, 1968 .... 46 ....... 20 ......... 4 ......... 8 ....... 74
Apr 07-09, 1980 .... 46 ........ 0 ......... 0 ......... 1 ........ 1
May .. 16, 1991 .... 46 ........ 3 ......... 0 ......... 0 ........ 0
May .. 07, 1993 .... 46 ........ 8 ......... 1 ......... 1 ........ 1
Apr .. 21, 1967 .... 45 ....... 20 ......... 4 ......... 3 ....... 58
Jun 07-08, 1984 .... 45 ....... 26 ......... 2 ......... 4 ....... 13
Nov .. 15, 1988 .... 44 ....... 13 ......... 0 ......... 3 ........ 7
Apr .. 29, 1984 .... 42 ........ 4 ......... 1 ......... 1 ........ 1
Feb 19-20, 1884 .... 41 ....... 37 ......... 4 ........ 28 ...... 167
May .. 29, 1980 .... 40 ........ 4 ......... 0 ......... 0 ........ 0
Dec .. 14, 1971 .... 40 ....... 10 ......... 0 ......... 2 ........ 2
Nov .. 07, 1995 .... 40 ........ 7 ......... 0 ......... 0 ........ 0

If there is a possible challenger to April 3-4, 1974 for most numerous outbreak (in the 1880-1995 period), it is May 20, 1949. Officially, only 36 tornadoes were reported that day, but that was before an organized reporting system existed. For the 1916-1949 period, tornado totals were only about one-fourth of what they are today. The newspaper headlines read "Tornado Army Hits Kansas." Clusters of small tornadoes, and a few large ones, also touched down in Oklahoma, Colorado, and Nebraska. May 20, 1949 was in the middle of a record period of activity, as significant tornadoes hit on nine consecutive days.

There have been other large outbreaks since 1995, but I haven't compiled them into a list to see how they compare to Grazulis's. According to the NOAA press release, April 3-4, 1974 (Super Outbreak) still holds the record for most tornadoes from one outbreak (148).

Thus, according to Grazulis's tornado outbreak definition, the April 26-28, 2011, "Dixie Alley Tornado Outbreak" will likely rank in 1st place all-time for total number of tornadoes, 2nd place for number of significant (EF2-EF5) tornadoes, and either 2nd or 3rd place for violent (F4/F5) tornadoes. We must wait for the final survey results to know for certain.

It would be interesting to perform a Destruction Potential Index (DPI) calculation for this outbreak as well:

THE DESTRUCTION POTENTIAL INDEX - A METHOD FOR COMPARING TORNADO DAYS by Richard L. Thompson and Michael D. Vescio

This outbreak would likely rank in 1st or 2nd place in history. Here are the DPI's for selected outbreaks (from their work):

1974 April 3 - 2647
1965 April 11 - 1632
1985 May 31 - 1338
1984 March 28 - 1301
1994 March 27 - 1292
1990 March 13 - 692
1991 April 26 - 644
1995 May 18 - 27

 

[Chris Hayes]

I've been curious as to if you could combine the 26th and 27th into one outbreak or not due to time differences between tornadoes; if the time lapse between tornadoes was too big or not. If not, then just the 26th and 27t is a prime contender for a pure tornado count. It won't beat out the Super Outbreak for violent tornadoes, but it could when it comes to tornado count.

EDIT: I've counted over 80 tornadoes on the Wikipedia write up for the 27th alone. I have yet to count up the 26th. Anyone know how many surveys are ongoing? I would think there would be quite a few surveys on going still

 

[Bobby Prentice]

I've been curious as to if you could combine the 26th and 27th into one outbreak or not due to time differences between tornadoes; if the time lapse between tornadoes was too big or not. If not, then just the 26th and 27t is a prime contender for a pure tornado count.

It's important to remember the definition of tornado outbreak that is being used here:

OUTBREAK...The term outbreak is used when referring to a group or family of six or more torndoes which are spawned by the same general weather system. Six tornadoes from two different thunderstorms cells, in advance of a cold front might be called a small outbreak. Six scattered tornadoes from different weather systems in three states should not be called an outbreak. This definition is from Galway (1977). Later that year, (personal conversation) he defined an outbreak of 10 ore more tornadoes from a single organized weather system. This book uses the six-tornado definition. The author has added the following addition to that definition: The end of one outbreak and the start of another is marked by a greater than six-hour lull in tornado activity, and an outbreak need not be confined to a single calendar day. Thus, if tornado activity subsides at 2 AM, and begins again at 2 PM, the Project considered that new activity to be the start of a different outbreak.

The definition of "tornado outbreak" is somewhat subjective by its very nature, but Tom Grazulis's definition (above) has a lot of documentation history and support from both the scientific (e.g., NSSL) and operational (NOAA/NWS) community.

 

[Dave Gallaher]

Very nice assembly, Bobby--thank you. One thing I'm wondering about is the number of paths crossing I 65 north of Birmingham. I mentioned in another thread that my drive to B'ham and back on Sunday revealed at least five or six obvious damage paths in Blount and Cullman Counties, along with some smaller and more isolated areas as well. These are in addition to older storm damage still evident from earlier in the year and last fall. I think the number will pick up once the biggest impacting storms are well documented and researchers get on the road.

On this radar (3:57CDT) there are some very small cells that are tor warned. Most of them had the stringbean appearance but developed couplets in their tail ends, moved some distance before being interfered with by bigger and more dominant cells. There are two of them here, south of Huntsville ( the + on the map); one is tor warned at this time:

 

[Drew.Gardonia]

has there been an official # of tornadoes released for each of the dates yet? Or are we still going off of storm "reports"?

 

[Drew.Gardonia]

wow, MSNBC reporting 312 in just one day (4/27/11)

http://www.msnbc.msn.com/id/42863493/ns/weather/

 

[rdale]

wow, MSNBC reporting 312 in just one day (4/27/11)

...and then you read "estimates"

 

[Ryan Wichman]

The soundings from this day are absolutely absurd. But what is truely amazing is the EF-5 Smithville Tornado proximity sounding taken from Tupelo, MS.

https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-snc6/229456_817020901705_30406759_39830364_7438221_n.jpg

Not only the 0-1 speed and directional shear of 60+knts. (Which was likely enchanced even more as is moved right along an effective warm front that was created by on-going convection). But the fact that this sounding had NO surface based CAPE. While the storm was likely pulling parcels from the much more bouyant airmass to the south, it was almost certainly not pulling them at the surface. Crazy to think about in a storm that produced an EF-5 monster and one that stayed on the ground for 132 miles none the less.

Goes to show how truely dynamic the lift in the atmosphere was.


I am still working on the post but I have also created a detailed timeline of the tornado outbreak that will continue to be updated.

http://convectiveaddiction.com/2011/04/29/april-27th-historic-tornado-outbreak-timeline

 

[John Peters]

The soundings from this day are absolutely absurd. But what is truely amazing is the EF-5 Smithville Tornado proximity sounding taken from Tupelo, MS.

https://fbcdn-sphotos-a.akamaihd.net/hphotos-ak-snc6/229456_817020901705_30406759_39830364_7438221_n.jpg

Not only the 0-1 speed and directional shear of 60+knts. (Which was likely enchanced even more as is moved right along an effective warm front that was created by on-going convection). But the fact that this sounding had NO surface based CAPE. While the storm was likely pulling parcels from the much more bouyant airmass to the south, it was almost certainly not pulling them at the surface. Crazy to think about in a storm that produced an EF-5 monster and one that stayed on the ground for 132 miles none the less.

Goes to show how truely dynamic the lift in the atmosphere was.


I am still working on the post but I have also created a detailed timeline of the tornado outbreak that will continue to be updated.

http://convectiveaddiction.com/2011/04/29/april-27th-historic-tornado-outbreak-timeline

This sounding probably sampled a cold pool associated with ongoing thunderstorms in the area. Based on SPC meso-analysis archive, there looks to have been plenty of SBCAPE in the area. Keep in mind as well - low level storm relative winds were pretty strong and southerly, so all of these storms were ingesting a steady flow of CAPE from the south.

 

[John Farley]

As time permits, I am trying to compile a spreadsheet of all the tornadoes documented by damage surveys. Not an easy task since the surveys keep getting updated, and because multiple tornado tracks straddle more than one CWA, and the surveys on these are getting completed at different times by different CWAs. Nonetheless, I can say with confidence that approximately 85 different tornadoes have been confirmed by the 5 most impacted NWS offices, Birmingham, AL; Huntsville, AL; Memphis, TN; Morristown, TN; and Jackson, MS. Surveys are ongoing in several of these areas and more tornadoes will likely be confirmed, and I have yet to compile tornadoes from any of the other numerous CWAs that were impacted to a lesser degree. At this point, I do think that it will be a record outbreak in terms of the number of confirmed tornadoes, although it is important to keep in mind that due to chasers, spotters, doppler indications of potential tornado locations, and systematic damage surveys, tornadoes today are more likely to be documented and entered into the record than tornadoes in past outbreaks, especially as you go farther back in time. So yes, this will likely be a record, but it may not in fact have involved more tornadoes than some of the largest outbreaks in the past.

Once my spreadsheet is closer to being complete, I will post it to my Website and will post again here when I do.

 

[Andrew Burnett]

I am still working on the post but I have also created a detailed timeline of the tornado outbreak that will continue to be updated.

http://convectiveaddiction.com/2011/04/29/april-27th-historic-tornado-outbreak-timeline

Great work.. nice recap.

 

[John Farley]

OK - here's the spreadsheet listing information on all of the tornadoes I have found thus far - 151 of them - that have been confirmed by official NWS damage surveys:

http://www.johnefarley.com/tornadotracks04-2011.htm

Undoubtedly, others will be confirmed without damage surveys (i.e. trusted spotter reports, video evidence, etc.), so this is likely a minimum number. If you see any errors or know about tornadoes confirmed by damage surveys that I don't have here, please send me a PM - preferably with a link to the correct information.

 

[John Massura]

According to this link: http://news.blogs.cnn.com/2011/05/04/record-178-tornadoes-from-south-storms/

The NWS is indicating this outbreak (officially?) surpasses the April 1974 event, and includes the 27th/28th only at this time. I haven't found anything at quick glance on the NOAA website yet.

 

[Jeff Wright]

We were also struck hard on the 15th of April. Footage at www.alabamawx.com (scroll down several pages) of a video shot from a tugboat if memory serves. I would realy like to see some top end researchers chase in my state.

I've heard all the excuses--our trees are all Redwoods and our mountains are the Himalayas--I get it. Two things to note. I don't think you will have to drive as far during a red-letter day, driving almost to Canada and what not. There are plenty of areas in my state of Alabama that are flat enough for DOW, if they would just come here. Also, I would think that the roads would be filled with less yahoos here, though I'm told that is questionable and that 'chasers' may have been killed in this storm-or at least folks with camera equipment in the car.

It is a challenge to spot storms here, but I think it might be worth studying. All that is being done is the study of those storms on the high plains.

Bobby, I see from the map that some of the tracks seem to begin at the Alabama state line. Is that an artifact, or was my state just that unlucky?

 

[rdale]

I would realy like to see some top end researchers chase in my state.

How do you think Alabama tornadoes differ from Oklahoma tornadoes? Plus WAY too many trees, hills, and too few observing platforms already in place. It makes no sense.