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TRANSCRIPT
9/5/2007
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S O U T H E A S T S E V E R E S T O R M S S Y M P O S I U M
A Rare Early Fall Case ofNon-Tropical Tornadic
Supercells in North Alabama
Brian Carcione, David Nadler, and Andy Kula
National Weather Service, Huntsville, AL
Saturday, March 24, 2007
Photo taken 22 Sept 2006 near Albertville (Marshall County) – courtesy Jessica Rutherford (Union Grove)
S O U T H E A S T S E V E R E S T O R M S S Y M P O S I U M
Overview
• Event Summary: 22 September 2006
• Fall Tornado Climatology
• Synoptic Pattern
• Model Output
• Mesoscale Analysis
• Brief Examination of Radar Data
• Storm Photography and Interpretation
• Conclusions/Lessons Learned
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Visible satellite image, 1615 UTC 9/22/06
Event Summary: 22 Sept 2006
• Multiple supercells along 3 favored
tracks
• 7 confirmed tornadoes, ranging from F-
0 to F-2; all F-1 and F-2 tornadoes struck
northeast Alabama
• Two tornadoes struck small cities
directly (Oneonta and Albertville)
Visible satellite image, 2115 UTC 9/22/06
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Tennessee Valley Tornado ClimatologyData compiled by Kurt T. Weber
Tornadoes Spawned by Non-Tropical Systems Affecting
the HUN CWA: 1950 - 2006
0
10
20
30
40
50
60
70
80
Jan Feb Mar Apr May Jun July Aug Sept Oct Nov Dec
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Early Fall Non-Tropical Tornado Climatology
Aug. - Oct. Tornadoes Spawned by Non-Tropical Systems Affecting
the HUN CWA - 1981- 2006
0
1
2
3
4
5
6
1981
1982
1983
1984
1985
1986
1987
1988
1989
1990
1991
1992
1993
1994
1995
1996
1997
1998
1999
2000
2001
2002
2003
2004
2005
2006
0
1
2
3
4
5
6
1950
1951
1952
1953
1954
1955
1956
1957
1958
1959
1960
1961
1962
1963
1964
1965
1966
1967
1968
1969
1970
1971
1972
1973
1974
1975
1976
1977
1978
1979
1980
August through October, 1950-2006Data compiled by Kurt T. Weber
Total of 7 tornadoes
1950-1996
Another 8 tornadoes
2002-2004
*
* Does not include
recently-confirmed
F-0 tornado in
Belgreen
13 additional tornadoes
associated with T.S.
Danny in 1985
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Synoptic Pattern – 300MB
1200 UTC 22 Sept and 0000 UTC Sept 23
300 MB Analysis
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Synoptic Pattern – 500MB
500 MB Analysis: 1200 UTC 22 Sept and 0000 UTC Sept 23
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Synoptic Pattern – 850MB
1200 UTC 22 Sept and 0000 UTC Sept 23
850 MB Analysis
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Synoptic Pattern – Surface
SPC Surface Maps: 12 UTC / 22 Sept 2006 and 00 UTC / 23 Sept 2006
LL HH
LL
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Synoptic Pattern – Surface
SPC Surface Maps: 12 UTC / 22 Sept 2006 and 00 UTC / 23 Sept 2006
LL HH
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Model Data: 06UTC 12km NAM-WRF
Model Run Accumulated Precip
18 UTC 9/22/07
Axes of convection forecast to NW and S of HUN forecast area
Surface Temperature and Wind
18 UTC 9/22/07
Uniform southerly flow (some SE flow in GA) with surface temps low to mid 70s (rain-cooled air)
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Model Data: NAM-WRF Soundings06 UTC NAM
valid 21 UTC
KHSV
Precipitable
Water: 1.66 in.
CAPE: 920 J/Kg
CIN: -31 J/Kg
LCL: 2337 ft AGL
0-3km SRH: 297
m2/s2
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SPC Day 1 Outlooks
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Morning Convection1200, 1500, and 1800 UTC 22 Sept
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Surface Analysis1800 UTC 22 Sept LAPS Analysis: Temperature and Dewpoint and Wind
Signs of secondary warm front or boundary from morning
convection across north/central Alabama
KTUP: 87/72
K4A9: 75/66
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Surface Analysis2100 UTC 22 Sept LAPS Analysis: Temperature and Dewpoint and Wind
Still indications of boundary, moved further east
KMSL: 81/72 (rain-cooled from
88/72)
K4A9: 79/70
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Surface Analysis
Lingering low
level boundary
from earlier
convection
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“Observed” Sounding (LAPS)21 UTC
KHSV
Precipitable
Water: 1.90 in.
CAPE: 2654 J/Kg
CIN: -1 J/Kg
LCL: 2440 ft AGL
0-3km SRH: 295
m2/s2
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1930 UTC Mesonet Analysis
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21 UTC SPC Mesoanalysis
1 km Energy Helicity Index
LCL Height
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21 UTC SPC Mesoanalysis
Precipitable Water
Deep-layer moisture
convergence
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21 UTC SPC Mesoanalysis
0-3 km mixed-layer CAPE,
Surface Vorticity
0-1 km storm-relative helicity
and storm motion
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Reviewing Storm Reports
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Storm-Scale & Photographic Analysis
KHTX 0.5º reflectivity, 2332Z
Leighton, AL
Arab, AL
Douglas, AL
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Classic Supercell Schematics
From Doswell and Burgess, 1993
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Douglas-Boaz supercell 2315Z
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Between Boaz & Douglas, Alabama: 621 pm
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Arab, Alabama
2142 UTC 22 Sept 2006
Southern Marshall County
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Arab, Alabama
2142 UTC 22 Sept 2006
Southern Marshall County
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Arab, Alabama: 438 pm
Along Highway 69 near Arab –
southern Marshall County
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Leighton, Alabama
2200 to 2227 UTC 22 Sept
Northeast Colbert County
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Leighton, Alabama
2200 to 2227 UTC 22 Sept
Northeast Colbert County
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Reflectivity Cross Section 2331Z
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Leighton, Alabama
Town Creek (5 miles east of Leighton) Town Creek (looking east)
Near Leighton – east central Colbert County
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Near Town Creek looking from north of Courtland, Alabama
Same storm, from Tuscumbia, AL
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Conclusions & Lessons Learned
• This was an almost entirely mesoscale-driven event.
• Mesoscale model output was poor in handling a few
key parameters, which happened to converge to
create a higher tornado threat.
• A mesoscale boundary played a major role in
enhancing streamwise vorticity across northeast
Alabama, which aided in tornadogenesis (especially
compared to similar cells in northwest Alabama).
• Forecasting these boundaries is very difficult, but
identifying them during an event is critical.