An Examination of the 22 May 2004 Hallam, Nebraska Tornado

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An Examination of the 22 May 2004 Hallam,
Nebraska Tornado

• Rebecca Adams
• Creighton University and WFO Omaha/Valley,
  Nebraska

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(No Transcript)
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Event Description
Hallam Supercell

• supercell formed in southwest Thayer county
  shortly after 23Z
• first severe report 2345Z
• 2.00 hail (as large as 3.00)
• tornadic by 2352Z
• report near 3 NW Hebron

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Radar Imagery
NWS Omaha/Valley WSR-88D radar
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Radar Imagery
Palmyra
Hallam
Daykin
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Radar Imagery

• 78.2 kts away
• 105.9 kts toward

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Event Description
Hallam Tornado

• Touchdown 0030Z
• Daykin, NE
• Lifted 0210Z
• Palmyra, NE
• Length 52 mi.
• 1 hr. 40 min.
• Max width 2.5 mi.

Map and information taken from storm survey
conducted by NWS Omaha/Valley and Emergency
Management
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Damage from Hallam tornado

• South of Hallam

• Near Firth

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Event Description
Two Supercells
Supercell A
Supercell B
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Event Description
Two Supercells why the difference?
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Synoptic Environment
Upper Levels

• 200 mb
• left exit quadrant of jet max
• 500 mb
• Southwesterly flow sharp trough over western
  U.S.
• shortwave evident in both 12Z, 00Z RUC
• 50 kt wind max
• positive vorticity advection apparent by 18Z
• cold air advection

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Synoptic Environment
200 mb

• heights
• winds
• isotachs

18Z RUC80 22 May
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Synoptic Environment
500 mb

• heights
• vorticity

00Z RUC80 23 May
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Synoptic Environment
Lower Levels

• 700 mb
• moisture advection 3.43 g/kg over 3 hrs
• warm air advection (isentropic lift) maximum over
  south central Nebraska 18Z onward
• 850 mb
• strong low level jet (40 kt max at 01Z)
• warm air, moisture advection maximums

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Synoptic Environment
310 K Surface

• pressure
• winds (streamlines)

00Z RUC
23 May
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Synoptic Environment
700 mb

• heights
• winds
• temperature
• temperature advection

00Z RUC80 23 May
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Synoptic Environment
850 mb

• temperature
• winds
• isotachs

01Z RUC40 23 May
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Synoptic Environment
925 mb

• winds
• theta-e

00Z RUC40 23 May
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Synoptic Environment
Surface

• strong low pressure over NW Kansas
• warm front across Nebraska into southern
  Minnesota
• dryline west-central KS
• outflow boundary
• warm temperature axis west of moisture pool
• 70 dewpoints

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Synoptic Environment
Surface

• METARs
• SLP
• temperature
• dewpoint

00Z RUC40 23 May
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Synoptic Environment

• Four lifting mechanisms
• Upper-level divergence from jet streak
• DPVA from strong shortwave
• Convergence along warm front, outflow boundary
• Isentropic lift

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Mesoscale Conditions
Tornado A1

• SBCAPE
• 3231 J/kg
• SBCIN
• -110 J/kg
• LCL
• 1176 m
• LFC
• 2213 m

22Z 22 May
modified RUC40
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Mesoscale Conditions
Tornado B3

• SBCAPE
• 4088 J/kg
• SBCIN
• -29 J/kg
• LCL
• 1001 m
• LFC
• 1350 m

00Z 23 May
modified RUC40
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Mesoscale Conditions
Comparison
SPC Mesoanalysis page Surface-modified RUC40
sounding at hour closest to tornado touchdown
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Thermodynamics
Comparison of Hallam Tornado to the A Set
A3
A4
A2
A1
A5
Start
End
A6
Mid

• Jon Daviess parameters for good or strong
  support of supercell tornadoes
• LFC 2000 m
• CIN -100 J/kg

http//members.cox.net/jondavies1/tornado_fcsting/
sprcll_tors.htm
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Thermodynamics
Comparison of Hallam Tornado to the A Set

• red lines 50th percentile of that parameter in
  the significant tornado class (F2-F5) as per
  Davies
• blue lines 75th percentile

Davies, J., 2004 Estimations of CIN and LFC
Associated with Tornadic and Nontornadic
Supercells. Wea. Forecasting, 19, 714-726.
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Low-Level Shear
Supercell B
0-1 km SRH
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Conclusions
Hallam Tornado

• Very favorable synoptic situation
• abundant lift
• cold air advection upper levels/warm, moist air
  advection lower levels
• cap weakened enough
• low-level shear outstanding

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Conclusions
Supercell Comparison

• Mesoscale environment can vary widely over small
  distances and times
• Height of LFC and amount of CIN key
• Low-level shear profile important
• Be on the lookout for very small-scale changes

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Acknowledgements

• NWS Omaha/Valley for providing AWIPS data
• Dan Nietfeld and Cathy Zapotocny for helpful
  insights
• Matthew Bunkers for the Excel Hodograph Program