cool season strong tornadoes in the southeast united states jared l. guyer noaa/nws storm prediction...
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Cool Season Strong Tornadoes in Cool Season Strong Tornadoes in the Southeast United Statesthe Southeast United States
Jared L. GuyerJared L. GuyerNOAA/NWS Storm Prediction Center
E-mail: [email protected]
March 1, 2007 – National Severe Weather Workshop
Early Morning Florida Early Morning Florida Tornadoes Tornadoes February 2, 2007February 2, 2007
Images courtesy NWS Melbourne
The Villages / Lady Lake Tornado
EF-3 Tornado with a 16.5 mile track and 8 Fatalities
3:08 a.m. – 3:25 a.m. EST
Lady Lake Church
Mobile Homes Demolished in Lady Lake
Early Morning Florida Early Morning Florida Tornadoes Tornadoes February 2, 2007February 2, 2007
Images courtesy NWS Melbourne
Lake Mack / Deland Tornado
EF-3 Tornado with 26 mile track and 13 Fatalities
3:37 a.m. – 4:10 a.m. EST
Motor Home Destroyed at Lake Mack
Mobile Home Frame at Lake Mack
IntroductionIntroduction
An ongoing SPC study to help identify a An ongoing SPC study to help identify a set of patterns, parameters, and set of patterns, parameters, and conditions that are commonly associated conditions that are commonly associated with the development of cool season with the development of cool season tornadoes in the Southeast States, with a tornadoes in the Southeast States, with a focus on strong (F2+ greater) tornadoes.focus on strong (F2+ greater) tornadoes.
Will also discuss some non-Will also discuss some non-meteorological aspects of these tornado meteorological aspects of these tornado occurrencesoccurrences
Study IntroductionStudy Introduction
68% of all December through February 68% of all December through February tornadoes in US occur in southeast (Galway tornadoes in US occur in southeast (Galway and Pearson 1981)and Pearson 1981)
Cool-season conditionsCool-season conditions Favorable wind shear common, however…Favorable wind shear common, however… Instability usually questionable ingredient for Instability usually questionable ingredient for
supercell developmentsupercell development Uncertainty regarding low-level moisture Uncertainty regarding low-level moisture
and atmospheric instability can make and atmospheric instability can make forecasting such events quite challenging forecasting such events quite challenging for operational forecasters (Vescio and for operational forecasters (Vescio and Thompson 1993).Thompson 1993).
Project DefinitionsProject Definitions ““Cool-Season”Cool-Season”
October 15 – October 15 – February 15February 15
Examined 20 Examined 20 cool seasonscool seasons 1984-1985 1984-1985
through 2003-through 2003-20042004
““Strong tornado”Strong tornado” F2+ intensityF2+ intensity
Focus on non-Focus on non-tropical systemstropical systems
Cool Season F2+ Cool Season F2+ TornadoesTornadoes
All F2-F5 Tornadoes between October 15 - February 15 from 1984-1985 to 2003-2004
239 F2+ Tornadoes (F2 76%, F3 20%, F4 4%, F5 0%) from 100 tornado days Long term yearly average: 12 F2+ tornadoes amongst 5 tornado days each year
Tornado Tracks in Red
Research MethodologyResearch Methodology Past Upper Air DataPast Upper Air Data
North America Regional Reanalysis (NARR) data at North America Regional Reanalysis (NARR) data at 6 hour intervals (00 UTC, 06 UTC, 12 UTC, 18 6 hour intervals (00 UTC, 06 UTC, 12 UTC, 18 UTC)UTC)
Mandatory level winds, geopotential heights, and Mandatory level winds, geopotential heights, and temperaturestemperatures
Precipitable water, surface temperature, surface Precipitable water, surface temperature, surface dewpointdewpoint
MSLP, 0-3 km helicity, lowest 180 mb most MSLP, 0-3 km helicity, lowest 180 mb most unstable CAPE (MUCAPE)unstable CAPE (MUCAPE)
Proximity Upper Air SoundingsProximity Upper Air Soundings Constraints of 200 km and +- 3 hrConstraints of 200 km and +- 3 hr 57 soundings amongst 50 tornado days57 soundings amongst 50 tornado days Modified for nearest surface inflow observation of Modified for nearest surface inflow observation of
temperature, dewpoint, and wind speed/direction temperature, dewpoint, and wind speed/direction with 0-1 hr preceding the tornadowith 0-1 hr preceding the tornado
Research Findings – 500 mb Research Findings – 500 mb PatternsPatterns
72% of cases associated 72% of cases associated with the anticyclonic with the anticyclonic south fringe of a 500 mb south fringe of a 500 mb jetjet
20% of cases coincided 20% of cases coincided with the 500 mb jet nose with the 500 mb jet nose and/or beneath the jet and/or beneath the jet axisaxis
Strength of the mid/upper Strength of the mid/upper level jet did not appear to level jet did not appear to discriminate between discriminate between isolated strong tornado isolated strong tornado events vs. larger events vs. larger outbreaksoutbreaks
Example 500 mb - 12 UTC 24 November 2001
14 F2+ Tornadoes
Example Upper Air SoundingExample Upper Air SoundingObserved RAOB preceding (23z XMR) the February 2,
2007 Tornadoes
Deep moisture
68 F Temp 66 F Dewpoint
Extremely strong wind
fields favorable for
rotating storms
Each Bar = 10 kt Each Flag = 50 kt
Modest Convective Instability
(CAPE)
Height (km)
Dewpoint
Temperature
Surface Dewpoint - Gulf Coast F2+ Tornadoes
63
71
61
69
66
58
62
66
70
74
°F
80%
Southeast Cool Season F2+ Southeast Cool Season F2+ TornadoesTornadoes
Surface Dewpoints (°F) Precipitable Water (inches)
Precipitable Water - Gulf Coast F2+ Tornadoes
1.28
1.80
1.48
1.18
1.67
1.00
1.10
1.20
1.30
1.40
1.50
1.60
1.70
1.80
1.90
Inch
es50%Mean Value
Derived from upper air soundings in proximity to F2+ Tornado Events
90th Percentile
10th Percentile
25th Percentile
75th Percentile
Southeast Cool Season F2+ Southeast Cool Season F2+ TornadoesTornadoes
CAPE (J/kg)
CAPE - Gulf Coast F2+ Tornadoes
1298
870676
2927
2215
2453
1618
1307 1277
615
331
109
2246
1695 1705
0
500
1000
1500
2000
2500
3000
3500
MUCAPE 100 mb MLCAPE SBCAPE
J/k
g
Derived from upper air soundings in proximity to F2+ Tornado Events
Southeast Cool Season F2+ Southeast Cool Season F2+ TornadoesTornadoes
25 F2+ Tornadoes in November-February associated with < 500 J/kg MLCAPE in 2003-2005
Storm environment data provided by Schneider and Dean, SPC
Southeast Cool Season F2+ Southeast Cool Season F2+ TornadoesTornadoes
Vertical Shear (kt) Storm Relative Helicity (m2/s2)
Vertical Shear- Gulf Coast F2+ Tornadoes
45
33
27
68
51
40
51
39
32
39
25
21
61
44
36
10
20
30
40
50
60
70
80
0-6 km Bulk Shear 0-3 km Bulk Shear 0-1 km Bulk Shear
kno
ts
Storm Relative Helicity (SRH) - Gulf Coast F2+ Tornadoes
208 200
403
332309
246
151
109
345
292
50
100
150
200
250
300
350
400
450
0-3 km SRH 0-1 km SRH
m2/s
2
Derived from upper air soundings in proximity to F2+ Tornado Events
Gulf Buoy Data Preceding Cool Season F2+ Gulf Buoy Data Preceding Cool Season F2+ TornadoesTornadoes
Evans and Guyer 2006
Surface Dewpoint
with Tornado Time Preceding the Tornado
Buoy 42002 Dewpoint Preceding Tornado Event
Gulf of Mexico Buoy
data (#42002) Preceding
F2+ Tornadoes in
the Cool Season
18 UTC BMX 16 Dec 2000 18 UTC BMX 16 Feb 2001
Meteorological CaveatsMeteorological Caveats Parameters Alone Parameters Alone
Don’t Tell the Whole StoryDon’t Tell the Whole Story
Tornadic Tornadic supercell supercell (F4 at TCL)(F4 at TCL)
Bow Echo/ Bow Echo/ DerechoDerecho
Slide courtesy Steve Weiss, SPC
Meteorological SummaryMeteorological Summary Similar to previous studies, confirmed the predominance Similar to previous studies, confirmed the predominance
of high shear/low instability regimes with cool season of high shear/low instability regimes with cool season Southeast U.S. F2+ tornadoesSoutheast U.S. F2+ tornadoes
Pronounced speed shear component in the lowest few Pronounced speed shear component in the lowest few kmkm 850 mb wind speeds typically >40 kt850 mb wind speeds typically >40 kt 0-1 km bulk shear >25 kt0-1 km bulk shear >25 kt
Only modest amounts of convective instability is Only modest amounts of convective instability is typically neededtypically needed CAPE values may be 500-1000 J/kg or lessCAPE values may be 500-1000 J/kg or less
Given a favorable synoptic system (and associated wind Given a favorable synoptic system (and associated wind fields), measures of low level moisture (dewpoints and/or fields), measures of low level moisture (dewpoints and/or mixing ratios) appear to be paramount for anticipating mixing ratios) appear to be paramount for anticipating Southeast U.S. F2+ tornadoes during the cool season.Southeast U.S. F2+ tornadoes during the cool season.
Cool Season F2+ Cool Season F2+ TornadoesTornadoes
All F2-F5 Tornadoes between October 15 - February 15 from 1984-1985 to 2003-2004
Tornadoes by Time
0
5
10
15
20
25
30
Nu
mb
er
of
To
rnad
oes
F4
F3
F2
Midnight
Overnight Cool Season Overnight Cool Season TornadoesTornadoes
Since November 2006, Since November 2006, 88% of tornado of tornado fatalities have occurred during the overnight fatalities have occurred during the overnight hourshours 30 nighttime fatalities30 nighttime fatalities (of 34 total) associated (of 34 total) associated
with 5 killer tornadoeswith 5 killer tornadoes Lady Lake, FL and Paisley/DeLand, FL on February 2, Lady Lake, FL and Paisley/DeLand, FL on February 2,
2007 (20 fatalities total)2007 (20 fatalities total) Gentilly, LA on February 13, 2007 (1 fatality)Gentilly, LA on February 13, 2007 (1 fatality) Riegelwood, NC on November 16, 2006 (8 fatalities)Riegelwood, NC on November 16, 2006 (8 fatalities) Montpelier, LA on November 15, 2006 (1 fatality)Montpelier, LA on November 15, 2006 (1 fatality)
Since 1998, the biggest single killer tornado Since 1998, the biggest single killer tornado was November 6, 2005 in Evansville, IN at was November 6, 2005 in Evansville, IN at 2:00 am CST (25 fatalities)2:00 am CST (25 fatalities)
Non-Meteorological Non-Meteorological FactorsFactors A tendency for events to occur during the late evening/overnight A tendency for events to occur during the late evening/overnight
hours during the cool season in the southeast United Stateshours during the cool season in the southeast United States Getting the message out before most people go to sleep – late Getting the message out before most people go to sleep – late
evening news?evening news? What late night precautions do people take?What late night precautions do people take? NOAA Weather RadioNOAA Weather Radio
Even in more modest scenarios (i.e. not a larger outbreak), the Even in more modest scenarios (i.e. not a larger outbreak), the potential may exist for strong tornadoes in a more isolated sense potential may exist for strong tornadoes in a more isolated sense given the conditions (i.e. strong wind shear)given the conditions (i.e. strong wind shear) A low probability and/or coverage, but it may be a high end A low probability and/or coverage, but it may be a high end
eventevent Scenario leads to an inherent tendency for occasional false Scenario leads to an inherent tendency for occasional false
alarmalarm Expected severe coverage may not be particularly high, but Expected severe coverage may not be particularly high, but
conditional potential exists for a strong tornado conditional potential exists for a strong tornado
Public education of the caveats associated with such cool Public education of the caveats associated with such cool season/nocturnal scenariosseason/nocturnal scenarios
A large part of a tornado watch may not end up experiencing A large part of a tornado watch may not end up experiencing widespread severe weather, but there is conditional widespread severe weather, but there is conditional potential for strong tornadoes where supercells occur in the potential for strong tornadoes where supercells occur in the watch watch
SummarySummary Future Research:Future Research:
Focus on solely hail/wind, and possibly Focus on solely hail/wind, and possibly weak tornado, events to derive a separate weak tornado, events to derive a separate proximity sounding dataset for proximity sounding dataset for comparative purposes. (Summer 2007)comparative purposes. (Summer 2007)
Closer examination of moisture return Closer examination of moisture return trends via buoy data and surface data.trends via buoy data and surface data.
My coauthors on this study:My coauthors on this study: David A. ImyDavid A. Imy, NOAA/NWS Storm Prediction Center, NOAA/NWS Storm Prediction Center Amanda KisAmanda Kis, University of Wisconsin, University of Wisconsin
2005 NOAA Hollings Scholarship program2005 NOAA Hollings Scholarship program Kar’retta VenableKar’retta Venable, Jackson State University, Jackson State University
2005 Research Experiences for Undergraduates (REU)2005 Research Experiences for Undergraduates (REU)
Cool Season Strong Tornadoes in Cool Season Strong Tornadoes in the Southeast United Statesthe Southeast United States
Jared L. GuyerJared L. GuyerNOAA/NWS Storm Prediction Center
E-mail: [email protected]
March 1, 2007 – National Severe Weather Workshop