# Presentation: 251577

## A Review of the North Alabama Violent Tornado Outbreak

**February 6, 2008**

- Brian Carcione & David Nadler
- NWS Huntsville, Alabama

**Notes:**
Introduction.  You’ll notice that, during this presentation, we never refer to the outbreak as the ‘Super Tuesday’ outbreak.  Our tornadoes occurred early in the morning on Wednesday.

## Overview

- Modified version of presentation given to 7th Annual Southeast Severe Storms Symposium
- Focus on warning decision-making (warning forecaster’s perspective)
- NWS NEXRAD Data
- ARMOR Data
- LMA in AWIPS and LMA trends
- Food for thought/points for discussion

## Local Event Overview

- “Storm Track Map” – MESH Data from NSSL

- EF-04:00 AM

- EF-14:43 AM

**EF-4****5:17 to 5:34 AM**

**EF-4**
**3:00 to 3:20 AM**

- EF-1

- EF-2

*No additional tornado damage**in Tennessee*

- EF-0

- EF-1

**Notes:**
This storm track map is actually derived from a hail detection algorithm, but it illustrates the supercell tracks very effectively (though they may be displaced slightly to the north).  The tornadoes tracks across western and middle Tennessee occurred during the evening hours, while those over Mississippi and Alabama occurred well after midnight.  It appears that the supercells producted EF-0 and EF-1 damage across east-central Mississippi.  The first cell moved across Lamar and Marion counties in Alabama, producing EF-1 damage near Beaverton; it then produced EF-4 damage across Lawrence and Morgan Counties.  The second storm, delayed by an hour or so and displaced to the south, produced a 25-mile swath of EF-2 damage across Tuscaloosa, Fayette, and Walker counties, a brief EF-0 touchdown south of Cullman, and a brief EF-1 touchdown just across the lake from Guntersville, Alabama.  It finally produced an EF-4 tornado in eastern Jackson County.  No further touchdowns occurred with either supercell, since they were absorbed into a trailing squall line.

## LAPS Surface Analysis

- Unseasonably warm air mass
- Temps at midnight were around 70°F with dewpoints in the low-mid 60’s
- Huntsville AL (HSV) Normals on Feb. 6th:52°F (Max) / 32°F (Min)

- 06Z Temperatures

**Notes:**
The light pink-shaded area reflects temperatures of 70 degrees or greater.  This analysis is from 06Z—or midnight—and temperatures are 70 degrees at midnight on the 6th of February, at a time when normal HIGHS are 52 degrees.  Dewpoints were in the low to mid 60s!  At the same time, there is a subtle convergence and thermal boundary along the Georgia-Alabama border, where temperatures fall into the middle 60s and dewpoints fall into the 50s.  Why were tornadic supercells not more rampant across the area earlier?

## 09 & 11Z UTC SPC Mesoanalysis

- 0-1km SRH & Storm Motion

- MLCAPE (contour) & MLCIN (shaded)

## Storm-scale / Radar Analysis

- 0600-1100UTC 06 Feb 2008 Radar Mosaic

**Notes:**
We will quickly step through the broader radar mosaic.  At 06Z, we were most concerned with the broken squall line extending across northern MS and west TN; a supercell was ongoing across middle TN.  There was some prefrontal convection occurring across north AL, but as noted earlier, the environment is capped so severe convection was unable to develop.  By 07Z, prefrontal convection over TN provides some inclination that conditions are destabilizing, but the squall line is showing no signs of becoming severe.  We are becoming concerned with the developing supercell across eastern Mississippi.  Of course, this will be the storm that produces the Lawrence County tornado.  Two hours later at 09Z, that supercell is producing the tornado, the squall line has advanced into north Alabama but remains below severe levels, and our second supercell is producing damage west of Birmingham.  By 11Z, the first supercell has been absorbed into the line in southern Tennessee, but the second cell has now rapidly moved into Jackson County, has already produced two tornadoes across the HUN CWFA, and is about to produce an EF-4.

## KGWX 0.5_1.3° BR/SRM - 0859Z 06 Feb 

- Lawrence County Tornado

**EF-4 tornado touching down around this time**

- KGWX 0.5° base velocity 100+ kt

**KGWX:** 62nm away, 0.5° angle elevation ~5700ft AGL

**Notes:**
This scan from GWX roughly reflects the time that the Lawrence County tornado is first touching down.  Due to the distance, the reflectivity does not show a classic supercell structure, though there is a subtle, shallow BWER noted at 1.5 degrees.  The SRM data shows moderate to strong but broad rotation, but the base velocity is more impressive; it indicates unbalanced rotation with velocities of more than 100 knots at 0.5 degrees, or almost 4,900 feet.

## KHTX 0.5_1.3° BR/SRM - 0906Z 06 Feb 

- KHTX 0.5_1.3° BR/SRM - 0906Z 06 Feb

- Lawrence County Tornado

- Rotational Velocity 109kt (81kt outbound, 28kt inbound)
- VR Shear = .0267 s-1

**KHTX:** 65nm away, 0.5° angle elevation ~7400ft AGL

**Notes:**
6 minutes later, the rotation is tighter and stronger, and reflectivity more impressive.

## UAH ARMOR Data – 0848-0907Z 06 FebData interrogated & visualized with GR2Analyst

- 0.7° Base Reflectivity and Velocity

**ARMOR:** 25-40nm away, 0.7° angle elevation ~2220-2970’ AGL

**81kt rotational velocity**

**Notes:**
The UAH ARMOR radar sampled the storm much more effectively and showed much greater reflectivity detail in the Lawrence County supercell than either NEXRAD ever did across the HUN CWFA.

## UAH ARMOR Data – 0912-0915Z 06 Feb

- 0.7° Base Reflectivity and Velocity

- 99kt Base Velocity at 1700’ AGL

**ARMOR:** 20-30nm away, 0.7° angle elevation ~1600-2000ft AGL

**Notes:**
The UAH ARMOR radar, located at HSV, is just 20 to 25 miles from the supercell at this time, and thus sampled the storm much more effectively.  The pendant is much more pronounced than from either NEXRAD and the velocity is more impressive...though there is missing data, and based on the other scans, I suspect the velocities may actually have maxed out.  Three minutes later, the reflectivity shows an even more pronounced hook, and velocity continues to show a strong unbalanced rotation displaced from the apex of the hook...and the peak velocity is 99 knots at just 1700 feet AGL.  Also of note is a secondary cell in both scans, and it will merge with the supercell over Decatur...and that is where the tornado lifts.

## LMA Data w/ KHTX Refl/SRM & LRM 

- Lawrence County Storm - 0840Z Feb06 2008

- Max source density ~ 36 as storm enters SW Lawrence County

- No tornado reported at this time

## LMA Data w/ KHTX Refl/SRM & LRM 

- LMA Data w/ KHTX Refl/SRM & LRM

- Lawrence County Storm - 0856Z Feb06 2008

- Source density jumps to ~ 61

## LMA Data w/ KHTX Refl/SRM & LRM 

- LMA Data w/ KHTX Refl/SRM & LRM

- Lawrence County Storm - 0902Z Feb06 2008

- Slight decrease in source density

- Tornado reported on the ground

## LMA Data w/ KHTX Refl/SRM & LRM 

- LMA Data w/ KHTX Refl/SRM & LRM

- Lawrence County Storm - 0906Z Feb06 2008

- 4 minutes later, source density diminishes significantly

- Tornado still on the ground

## Supercell-squall line merger

- EF-4 Tornado

## Lawrence County Storm Track

**All estimated*

**EF-4 Rating**
- Peak Wind 170 mph
- Path Length 16.7 miles
- Path Width 1⁄2 mile

## KHTX 0.5_1.3° BR/SRM - 1043Z 06 Feb 

- Jackson County Tornado

**Brief EF-1 touchdown just north of Guntersville, AL**

**Notes:**
Now onto the other supercell.  This scan is from 1043Z, around the time an EF-1 tornado briefly touched down just north of Guntersville, and it shows very strong, deep rotation and a much more ‘classic’ supercell reflectivity structure.

## KHTX 0.5_1.3° BR/SRM - 1115Z 06 Feb 

- Jackson County Tornado

**Notes:**
About a half-hour later, the reflectivity has weakened.  The SRM shows even stronger rotation though perhaps broader at 0.5, but the 1.3 scan shows tighter rotation, possibly indicative of the descending mesocyclone and tornadogenesis.

## KHTX 0.5_1.3° BR/SRM - 1125Z 06 Feb 

- Jackson County Tornado

- Rotational Velocity 132kts at ~ 1500ft AGL (70kt inbound, 62kt outbound)

- Enhanced reflectivity indicates possible debris detection

**Notes:**
Ten minutes later, the tornado is definitely on the ground; the reflectivity no longer shows the hook structure, but there is instead an area of enhanced reflectivities which may reflect debris.  The SRM, though, perhaps shows the most impressive image of the whole event—literally gate-to-gate shear, one pixel each of 70 knots inbound, 62 knots outbound, and this is probably as close to sampling the tornado itself as you will get with a NEXRAD.

## UAH ARMOR Data – 1118-1119Z 06 Feb

- 0.7° Base Reflectivity and Velocity

**ARMOR:** ~45nm away, 0.7° angle elevation ~3700-4600ft AGL

- 87kt rotational velocity at 3680’ AGL

- 84kt velocity

**Notes:**
ARMOR’s perspective on the Jackson County tornado is not as good because it is nearly twice as far away as KHTX is from the storm.  The reflectivity data appears to suffer from attenuation issues, but the velocity data appears to be reasonable (albeit not as high-quality due to the distance).  The rotation is nearly as strong as indicated by KHTX.

## LMA Data w/ KHTX Refl/SRM & LRM 

- LMA Data w/ KHTX Refl/SRM & LRM

- Jackson County Storm - 1032Z Feb06 2008

- Max source density ~ 105

- No tornado reports yet

## LMA Data w/ KHTX Refl/SRM & LRM 

- LMA Data w/ KHTX Refl/SRM & LRM

- Jackson County Storm - 1038Z Feb06 2008

- Significant decrease within 6 minutes

- EF-1 Tornado on the ground

- Reflectivity suggests a more ‘classic’ supercell structure with more impressive updrafts

## LMA Data w/ KHTX Refl/SRM & LRM 

- LMA Data w/ KHTX Refl/SRM & LRM

- Jackson County Storm - 1100Z Feb06 2008

- Big jump as storm ascends Sand Mountain

- No tornado on the ground at this time

- Reflectivity diminishing, perhaps becoming a lower-topped supercell

## LMA Data w/ KHTX Refl/SRM & LRM 

- LMA Data w/ KHTX Refl/SRM & LRM

- Jackson County Storm - 1125Z Feb06 2008

- Storm begins to weaken, supported by significant flash decrease

- EF-4 Tornado on the ground

- Enhanced “white” area possible debris being detected by 88D base reflectivity

## Ascending Sand Mountain

- EF-1 near Guntersville

- EF-4 Tornado

## Jackson County Storm Track

**All estimated*

**EF-4 Rating**
- Peak Wind 180 mph
- Path Length 10.9 miles
- Path Width 3/8 mile

## Food for Thought: ARMOR

- ARMOR samples most of the ‘central’ HUN CWFA better than any NWS NEXRAD
- Would have been more useful to ascertain reflectivity structure
- Has some unique limitations
- Many forecasters are eager to use and learn about the ARMOR data
- GR2Analyst makes it more readily available
- Dual-pol upgrade will make that data more accessable as well
- COMET partnership to make data available in AWIPS will be a key

## Food for Thought: LMA

- Tertiary data source during this event—radars, reports, upstream conditions, etc. were of greater importance
- HUN forecasters traditionally look for jumps/drops in LMA data based on earlier research (~2001-2004)
- This case does not disprove that, but does show weaknesses in an overly-simplistic methodology
- Cool season vs. warm season environments—not all storms are created equal
- Distance/sampling concerns similar to those with radar data
- Difficulty in visualizing & analyzing LMA data (trends, color tables, etc.)
- More research, better visualization techniques, training refreshers will help

## Questions or Comments?

**Brian.Carcione@noaa.gov**
**David.Nadler@noaa.gov**
- http://weather.gov/huntsville
*Thanks to Chris Darden and our NASA and UAH partners*