A Multiscale Analysis of the 23-24 November 2004 Southeast United States Tornado Outbreak

A Multiscale Analysis of the A Multiscale Analysis of the 23-24 November 2004 23-24 November 2004

Southeast United States Southeast United States Tornado OutbreakTornado Outbreak

Alicia C. WasulaAlicia C. Wasula

Event SummaryEvent Summary

23/1700 UTC – 24/1300 UTC 23/1700 UTC – 24/1300 UTC (nocturnal)(nocturnal)

80 Tornadoes (17 F2 or greater)80 Tornadoes (17 F2 or greater) 3 Fatalities / 38 Injuries3 Fatalities / 38 Injuries 45% tornadoes close to Gulf coast 45% tornadoes close to Gulf coast

(south of 32 (south of 32 N)N)

MotivationMotivation

Examine tornado episode from Examine tornado episode from synoptic/mesoscale perspective to synoptic/mesoscale perspective to look for similarities/differences to look for similarities/differences to composite Gulf coast tornado composite Gulf coast tornado episodeepisode

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11))Convective Available Potential Energy (CAPE, Convective Available Potential Energy (CAPE, J/kg)J/kg)

Johns et Johns et al. 1993al. 1993

CAPE vs. Shear for Cold Season Tornado CAPE vs. Shear for Cold Season Tornado CasesCases

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Johns et Johns et al. 1993al. 1993

CAPE vs. Shear for Warm Season Tornado CAPE vs. Shear for Warm Season Tornado CasesCases

Tornado Episode Tornado Episode CompositesComposites

NCEP/NCAR 2.5NCEP/NCAR 2.5x 2.5x 2.5 Reanalysis Reanalysis datasetdataset

All tornado episodes 1950-2001All tornado episodes 1950-2001 ‘‘Episode-relative’ compositeEpisode-relative’ composite Grouped by start time: 0000-0600, Grouped by start time: 0000-0600,

0600-1200, 1200-1800, 1800-0000 0600-1200, 1200-1800, 1800-0000 UTCUTC

Will show 0600-1200 UTC onlyWill show 0600-1200 UTC only

200 hPa height (m), isotachs (m s200 hPa height (m), isotachs (m s-1-1))

500 hPa hgt (m), avor. (x 10500 hPa hgt (m), avor. (x 10-5-5 s s-1-1), vort. adv. (x 10), vort. adv. (x 10-10-10 s s-2-2))

850 hPa hgt (m), temp (850 hPa hgt (m), temp (C), temp. adv. (x 10C), temp. adv. (x 10-5-5 C sC s-1-1))

1000 hPa height (m), 1000-500 thck. (dam), 700 hPa RH (%)1000 hPa height (m), 1000-500 thck. (dam), 700 hPa RH (%)

700 hPa height (m), vertical motion (x 10700 hPa height (m), vertical motion (x 10-3-3 hPa s hPa s-1-1))

850 hPa winds, 850 hPa winds, ee (K), 850-500 lapse rate ( (K), 850-500 lapse rate (C)C)

Summary: CompositesSummary: Composites

Strong signal in spite of large sample size:Strong signal in spite of large sample size: ULJ entrance region at 200 hPaULJ entrance region at 200 hPa Vigorous upstream trough at 500 hPaVigorous upstream trough at 500 hPa Southwesterly LLJ at 850 hPaSouthwesterly LLJ at 850 hPa Low-level Low-level ee ridge ridge

Surface composites show 1Surface composites show 1stst tornado occurs: tornado occurs: At strongest At strongest TT On northern edge of moisture surge/southerly On northern edge of moisture surge/southerly

flowflow Dew point anomalies > +8 Dew point anomalies > +8 CC

Case Study:Case Study:24 November 24 November

20042004

http://www.spc.noaa.gov

22 November 2004 0000 UTC

SLP, 1000-500 THCK 500 hPa HGHT, AVOR

200 hPa HGHT, ISOTACHS 850 hPa HGHT, e, ISOTACHS






















CAPE 1847 J/kgLI -70-6 km shear 38 kt0-2 km shear 18 ktSWEAT 400

JAN23/2100 UTC


JAN24/0000 UTC

CAPE 81 J/kgLI 30-6 km shear 39 kt0-2 km shear 22 ktSWEAT 225

JAN24/1200 UTC


LIX24/0000 UTC


LIX24/0600 UTC


LCH23/1800 UTC


LCH24/0000 UTC

Surface Analysis24 November 20040000 UTC





<>

IR24 November 20040615 UTC http://locust.mmm.ucar.edu




ConclusionsConclusions

Tornado episode occurred:Tornado episode occurred: In presence of strong synoptic-scale In presence of strong synoptic-scale

forcing for ascent (in warm sector)forcing for ascent (in warm sector) LLJ strength increased overnightLLJ strength increased overnight Surface winds stayed south or southeast Surface winds stayed south or southeast

as surface low rapidly deepened to the as surface low rapidly deepened to the northnorth

Ample moisture and instabilityAmple moisture and instability

ConclusionsConclusions

Case study shows similarities to composite Case study shows similarities to composite tornado episodetornado episode Strong shear/ULJ/LLJStrong shear/ULJ/LLJ Deepening surface cycloneDeepening surface cyclone Ample low-level moisture (esp. close to coast)Ample low-level moisture (esp. close to coast) Surface winds ‘back’ with time ahead of Surface winds ‘back’ with time ahead of

surface lowsurface low Difference:Difference:

Mesoscale thermal gradient?Mesoscale thermal gradient?

Future WorkFuture Work

Question:Question: Did isallobaric effects help to keep flow Did isallobaric effects help to keep flow

in warm sector southerly/southeasterly in warm sector southerly/southeasterly and allow warm moist Gulf air to remain and allow warm moist Gulf air to remain in place close to coast?in place close to coast?

Why did LLJ increase in strength so Why did LLJ increase in strength so rapidly?rapidly? Dynamically driven?Dynamically driven?

Documents

A Multiscale Analysis of the 23-24 November 2004 Southeast United States Tornado Outbreak