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: Jared.Guyer@noaa.gov

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: Jared.Guyer@noaa.gov

March 1, 2007 – National Severe Weather Workshop