Final stats from April 25th, 26th, 27th, and 28th, 2011 Tornado Outbreaks

April 2011 Storm Data has been out for a little while, and I finally got around to putting together a map of all tornadoes from April 25th-28th on Google Earth. For the purposes of this analysis, I broke the event down into two separate outbreaks. The first was April 25th-early 26th and the second was the afternoon of April 26th-27th-28th.


Map of all tornadoes for April 25th-28th, 2011. Light blue = EF0, green = EF1, brown = EF2, blue = EF3, pink = EF4, purple = EF5.

For April 25th/early 26th:
51 tornadoes total

20 EF0, 24 EF1 (44 weak), 5 EF2, 2 EF3 (7 strong & significant, 2 intense, 0 violent)

Total fatalities: 5

Deadly tornadoes (listed in order of most-least fatalities): 2
Vilonia, AR EF2 (4)
Walnut Valley, AR EF3 (1)

States affected: 8

Tornadoes by State:
Arkansas: 18
Texas: 17
Kentucky: 6
Missouri: 3
Indiana, Mississippi, Oklahoma, Tennessee: 2 each

Fatalities by State:
Arkansas: 5

Map of tornadoes from April 25th-early on the 26th. Light blue = EF0, green = EF1, brown = EF2, and blue = EF3.

For afternoon April 26th/April 27th/April 28th:
290 tornadoes total

100 EF0, 113 EF1 (213 weak), 43 EF2, 19 EF3 (62 strong), 11 EF4, 4 EF5 (77 significant, 34 intense, 15 violent)

Total fatalities: 317

Deadly tornadoes (listed in order of most fatalities to least fatalities): 29
Hackleburg/Phil Campbell/Oak Grove/Mt. Hope/Langtown/Tanner/Harvest, AL EF5 (72)
Tuscaloosa/Concord/Pleasant Grove/McDonald Chapel, AL EF4 (64)
Smithville, MS/Shottsville, AL EF5 (23)
Fyffe/Rainsville/Sylvania, AL EF5 (23)
Shoal Creek/Ohatchee, AL EF4 (22)
Ringgold, GA/Apison, TN EF4 (21)
Boley Springs/Oakman/Cordova/Sipsey, AL EF4 (13)
Pisgah/Higdon/Flat Rock/Shiloh, AL/Trenton GA EF4 (13)
Horse Creek, TN EF3 (8)
Sawyerville/Eoline, AL EF3 (7)
Raleigh/Enterprise/Rose Hill, MS EF4 (7)
Central/Lake Martin/Dadeville, AL EF4 (7)
Cullman/Ruth, AL EF4 (6)
Anchor/Houston/New Wren, MS EF3 (4)
New Harmony, TN EF4 (4)
Preston, MS EF5 (3)
Cleveland, TN EF2 (3)
Glade Springs, VA EF3 (3)
Butler, TN EF2 (2)
Vaughn, GA EF3 (2)
Barnesville, GA EF3 (2)
Mathison, MS EF2 (1) Hanceville, AL EF2 (1) Pisgah, AL EF1 (1) Lookout Valley, TN EF2 (1)
Cleveland, TN EF1 (1)
Bridgeport, AL EF4 (1)
High Rock, VA EF2 (1)
Lake Burton, GA EF3 (1)

Italicized tornadoes occurred with the early-morning QLCS.

Of the 290 tornadoes, approximately 80 (from best estimate) occurred with the early-morning QLCS/embedded supercells across LA, MS, AL, GA, TN, KY, and OH. This 5 EF3s, 23 EF2s, and the 4 killer tornadoes italicized above.

States affected: 21

Tornadoes by State:
Tennessee: 66
Alabama: 62
Mississippi: 39
Virginia: 19
Texas: 17
Louisiana, Georgia: 16 each
North Carolina: 13
Arkansas: 12
Maryland: 11
New York: 9
Kentucky, Pennsylvania: 7 each
South Carolina: 3
Florida, Missouri: 2 each
Michigan, Oklahoma, Ohio, Indiana, West Virginia: 1 each

Fatalities by State:
Alabama: 235
Tennessee: 32
Mississippi: 31
Georgia: 15
Virginia: 4

Map of tornadoes from the afternoon of April 26th through April 27th and into April 28th. Light blue = EF0, green = EF1, brown = EF2, blue = EF3, pink = EF4, purple = EF5.

Other statistics from the outbreak:

1200 UTC-1200 UTC tornado numbers
25/1200 UTC to 26/1200 UTC: 51 tornadoes
26/1200 UTC to 27/1200 UTC: 121 tornadoes
27/1200 UTC to 28/1200 UTC: 156 tornadoes
28/1200 UTC to 29/1200 UTC: 13 tornadoes

Largest tornado: Tuscaloosa/Birmingham, AL EF4 (up to 1.5 miles wide)
Longest-tracked tornado: Hackleburg/Phil Campbell et al., AL EF5 (132.1 miles long)
Number of tornadoes with >100 mile path lengths: 3 (Hackleburg/Phil Campbell EF5 132.1 miles, Cordova EF4 125 miles, Rose Hill EF4 124 miles)
Number of tornadoes with 50-99 mile path lengths: 6 (Ohatchee EF4 98 miles, Tuscaloosa/Birmingham EF4 81 miles, Sawyerville/Eoline EF3 72 miles, Cumberland EF3 59 miles, New Wren EF3 53 miles, Ringgold/Apison EF4 50 miles)

If you are interested in the whole .kmz file, email me at tony DOT lyza AT valpo DOT edu.

Why August 2nd might bring trouble

It's late (1:35 AM CDT as I start this) but I thought I'd post a few thoughts regarding tomorrow's intriguing setup for southern WI, northern IL, northern IN, and southern Lower MI.

The past several runs of the GFS and NAM have been consistent in creating a potentially robust severe weather environment across this region during the afternoon and evening hours on Tuesday. Several key factors are still in the air, but as we approach this potential event, we can try to shed some clarity on them.

1) Ongoing convection. Currently, there are two areas of convection ongoing upstream from the threat area. One is up in Minnesota and the other is in Iowa. Storm motion vectors and the theta-e gradient demarcating the moist, unstable airmass in place across the plains and lower Great Lakes from the more stable, drier airmass to the northeast and along which nocturnal complexes typically move, suggest that the complex in Minnesota, should it hold together, will likely slide across northern and eastern WI and across Lake Michigan into western MI as it begins to weaken tomorrow morning. Released from this MCS should be a decent outflow boundary that will likely skirt across the lake into eastern WI/northeastern IL/northwestern IN during the morning hours. By the time it reaches this point, item #2 will come into significant play.

2) Strong low-level wind shear and surface wind flow. The 12z NAM this morning had 35kt of wind at 925mb over NE IL at 21z Tuesday afternoon. That is simply incredible. Typically by August we are in the heart of the summer doldrums, where the jet stream weakens, overall atmospheric flow weakens, and thus we have overall just less wind in the atmosphere. The few times we get substantial low-level wind shear it is usually caused by the nocturnal low-level jet, a feature more common in the plains. There is certainly nothing nocturnal, however, about 21z (4 PM CDT). Additionally, sfc flow is progged to be up to 20kt! This will aid in providing healthy inflow into a northwest flow storm event, especially given that the sfc flow is from the SW. Additionally, that strong SW sfc flow is going to likely halt the progression of the outflow released by the morning convection. This should lead to the boundary stalling and slowly washing out, allowing for it to retain its vorticity-enhancing characteristics while storm-detrimental characteristics.

3) Strong instability. This comes with both pros and cons. It's going to be hot. Like, mid-90s hot. And it's going to be humid, likely extremely humid. Dew points often pool ahead of boundaries in the summer, and indeed both the GFS and the NAM pool dewpoints ahead of the front, with some areas progged to have 80°F or higher dewpoints tomorrow afternoon. This may be overzealous in spots, but with corn and soybeans really taking off this time of year, the potential to realize this is certainly there. This will lead to an extremely unstable airmass, with MLCAPE of 3500-5000J/kg in areas where cloud debris from the morning convection doesn't significantly hinder heating. Due to intense heating, however, there is the potential that LCL heights may rise up to 1250m, which is a potential negative to tornadoes. Wind-wise, however, higher LCLs would tend to actually increase the threat for downbursts/microbursts and significant wind damage.

4) Deep-layer shear. Deep-layer (0-6km) shear of 35-40kt is progged to be in play tomorrow. Additionally, these shear vectors run fairly perpendicular to the front. All this means that the deep-layer shear will likely be supportive of supercell structures for a time Tuesday afternoon/evening before storms congeal into an MCS.

Overall, the bottom line is this. It's impossible to point out the exactly location of greatest threat tomorrow. That will depend on where the current activity ends up. However, wherever the greatest threat is, it appears there will be a potential for supercells with hail, wind, and even tornadoes. There may even be an enhanced tornado threat *if* a supercell can favorably interact with the remnant outflow from the morning convection. Finally, even after an MCS forms, unseasonably strong low-level shear values dictate that mesovortex formation potential and subsequent tornado potential cannot be ignored.

Review of July 17th, 2011 LaMoure County, North Dakota, Tornado: An EXTRAORDINARY Mesoscale Environment

Two-panel image of °0.5 storm-relative mean radial velocity (L) and 0.5° base reflectivity from Aberdeen, South Dakota (KABR) radar at 2313z (6:13 PM CDT) Sunday, June 17th, 2011. Of note is that the TVS (tornado vortex signature) maxes out at 171 knots gate-to-gate and the reflectivity features a debris ball of 65dBz intensity. This is likely near the time that a farmhouse was reportedly completely destroyed west of Berlin, North Dakota. Level II image created on GRLevel2 Analyst Edition.

The year of 2011 has been no stranger to strong-violent tornadoes. From the three-day outbreak that ravaged areas from Tushka, Oklahoma, to Raleigh, North Carolina, on April 14th-16th, to what's being dubbed the second Super Outbreak of April 25th-28th, to the horrific Joplin, Missouri, EF5 killer on May 22nd, the United States has been no stranger to incredible tornado events this year. And though July 17th will likely go down as a fairly minor footnote in the 2011 record book, it was extraordinary in its own right.

Climatologically, strong-violent tornado activity peaks in April in the United States, with May and June the next closest contenders. July typically sees a tailoff in strong-violent tornadoes, but when they do occur, they most often occur in the northern plains and upper midwest. In this regard, the events of July 17th were far from extraordinary. In fact, they were exactly what would be expected this time of year.

What sets July 17th apart is the environment in which the supercell that produced the LaMoure County tornado developed. The combinations of exceptional instability, rather strong shear, a lift mechanism, and lack of thermonuclear cap created one of the most impressive mesoscale environments I have witnessed or studied.

Let's start with instability and forcing. With temperatures in the lower 90s and dewpoints in near 80 (no, that's not a misprint as you can see below), the stage was set for an incredibly unstable airmass to take shape. With the jet stream overhead helping to bring in cooler temperatures aloft, that was exactly what took place. Additionally, a boundary was in place across North Dakota, as evidenced by the wind shift at the sfc and the maximum in moisture convergence. This boundary would provide the focus for convection.

23z sfc map from SPC mesoanalysis.

Sfc moisture convergence from SPC mesoanalysis.

By 23z in the afternoon, an extraordinary amount of CAPE had built in across southern North Dakota. SBCAPE values of 8000J/kg or greater and MLCAPE values of an incredible 7000J/kg with MLCINH completely eroded were in place across southern North Dakota. Incredibly, as can be seen on the MLCAPE graphic, the supercell that produced the strong tornado had these incredible instability values directly within its near-storm environment, providing an incredible amount of fuel and updraft velocity to the storm.

SBCAPE from SPC mesoanalysis.

MLCAPE from SPC mesoanalysis.


RUC 1 hr fcst sounding from the 22z run for 23z on 7/17/11 near supercell location. Note lack of major capping inversion, low LCLs, and extreme lapse rates. Sounding from www.twisterdata.com

Also of note were high values of 0-3km CAPE and sfc vorticity in the near-storm environment. These high values, attributed to the 750-1000m LCLs and lack of low-level inversion to eliminate low-level instability, acted to rapidly accelerate near-sfc based parcels and to stretch the low-level vorticity into the updraft, aiding in tornadogenesis.

0-3km CAPE and sfc vorticity from SPC mesoanalysis. Note the higher regions of both values near the North Dakota supercell.

LCL heights from SPC mesoanalysis.

It is most typically the case that, when such tremendous instability is in place without a capped atmosphere, that vertical shear is extremely weak. This is because vertical shear is indicative of warm air advection in a layer, a process that typically, in hot environments, promotes capping. In North Dakota, however, significant amounts of shear were in place in the near-storm environment, with 40-50 knots of 0-6km shear and 150-200m**2/s**2 of 0-1km SRH. Additionally, the storm moved quite a bit to the right of the storm motion vector used to calculate the 0-1km SRH, thus increasing the actual amount of helicity available to the storm, as described below.

0-6km shear from SPC mesoanalysis.

0-1km SRH from SPC mesoanalysis.


22z RUC fcst hodo for 23z on the 17th. The shaded area represents a (very) rough approximation of 0-1km SRH. The green is for a storm moving along the given vector. The red is for the supercell as it turned to the right of the given vector. Note the increase in shaded area, indicating an increase in 0-1km SRH. Hodo from www.twisterdata.com

This combination of extreme instability and strong shear led to off-the-chart severe indicies, with effective-layer significant tornado parameter of 8 and 0-1km EHI of 8 in the near-storm environment.

Effective layer STP from SPC mesoanalysis.

0-1km EHI from SPC mesoanalysis.

All-in-all, with the boundary in place, minimal capping, strong shear, and incredible instability, the environment across southern North Dakota on July 17th was extraordinary. It is with great fortune that this storm did not strike a major population center, like many of the other major 2011 tornadoes.