wfo huntsville, alabama a review of the north alabama violent tornado outbreak february 6, 2008...

WFO Huntsville, AlabamaWFO Huntsville, Alabama

A Review of the North Alabama Violent Tornado Outbreak

February 6, 2008

Brian Carcione & David NadlerNWS Huntsville, Alabama

WFO Huntsville, Alabama

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-4EF-45:17 to 5:34 5:17 to 5:34

AMAM

EF-4EF-43:00 to 3:20 AM3:00 to 3:20 AM

EF-1

EF-2

No additional tornado damagein Tennessee

EF-0

EF-1


09 & 11Z UTC SPC Mesoanalysis

0-1km SRH & Storm Motion MLCAPE (contour) & MLCIN (shaded)


Storm-scale / Radar Analysis0600-1100UTC 06 Feb 2008 Radar Mosaic


KGWX 0.5_1.3° BR/SRM - 0859Z 06 Feb Lawrence County Tornado

EF-4 tornado touching down around this timeKGWX 0.5° base velocity 100+ kt

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


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


UAH ARMOR Data – 0848-0907Z 06 Feb

Data interrogated & visualized with GR2Analyst

0.7° Base Reflectivity and VelocityARMOR: 25-40nm away, 0.7° angle elevation ~2220-2970’ AGL

81kt 81kt rotational rotational velocityvelocity



0.7° Base Reflectivity and Velocity

99kt Base Velocity at 1700’ AGL

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


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



Source density jumps to ~ 61



Slight decrease in source density

Tornado reported on the ground



4 minutes later, source density diminishes significantly

Tornado still on the ground


Supercell-squall line merger

EF-4 Tornado


KHTX 0.5_1.3° BR/SRM - 1043Z 06 Feb Jackson County Tornado

Brief EF-1 touchdown just north of Guntersville, AL



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

Enhanced reflectivity indicates possible debris detection



0.7° Base Reflectivity and Velocity

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

87kt rotational velocity at 3680’ AGL

84kt velocity


LMA Data w/ KHTX Refl/SRM & LRM Jackson County Storm - 1032Z Feb06 2008

Max source density ~ 105

No tornado reports yet



Significant decrease within 6 minutes

EF-1 Tornado on the ground

Reflectivity suggests a

more ‘classic’ supercell

structure with more

impressive updrafts



Big jump as storm ascends Sand Mountain

No tornado on the ground at this time

Reflectivity diminishing,

perhaps becoming a

lower-topped

supercell



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 GuntersvilleEF-4 Tornado


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

WFO Huntsville, AlabamaWFO Huntsville, Alabama

Questions or [email protected]@noaa.gov

http://weather.gov/huntsville

Thanks to Chris Darden and our NASA and UAH partners

wfo huntsville, alabama a review of the north alabama violent tornado outbreak february 6, 2008...

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