July 22, 2003 The Mid South Derecho

1
July 22, 2003 The Mid South Derecho

• Scott McNeil, Dan Valle, Jonathan Howell, Greg
  Garrett
• National Weather Service - Memphis, TN

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July 22nd Derecho

• Scope and extent of the damage
• Meteorological aspects of the event
• Radar imagery

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Event Overview
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The Great Damage Corridor

• A series of violent downburst winds swept
  through the greater Memphis area

80-105 mph
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Facts

• Occurred on July 22nd during the early daylight
  hours
• 1 direct fatality and 6 indirect fatalities
• Wind gusts topped 100 mph
• 84 mph at Channel 3
• 61 mph at Airport
• 77 mph at Agricenter
• 102 mph at Autozone
• 500 Million in damage

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Major Power Outage
338,000 at peak (over 750,000 people)
My house
47,000 w/o power after 10 days (over 100,000
people)
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Facts

• Transportation was interrupted
• Worlds busiest freight airport and Northwest
  Airlines hub closed
• 75 of electric traffic signals didnt work
• Some communities lost water along with electricity

• Shelby county declared a federal disaster area by
  the President.

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Widespread Damage
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What is a Derecho ?Johns and Hirt 1987

• Area of wind damage and/or convective gusts 50
  kts or greater.
• Major axis length of at least 400 km.
• Reports must show chronological progression.
• There must be at least 3 reports separated by 64
  km or more, of either F1 damage or convective
  gusts of 65 kts or greater.
• No more than 3 hours can lapse between wind
  damage events.

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Types of DerechosJohns and Hirt 1987 , Johns
1993 (adapted from Barnes and Newton 1985)
Progressive
Serial
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Progressive Derecho EnvironmentJohns et al. 1990

• Surface Pattern
• East-west frontal boundary (genesis area
  frequently north of front).
• Strong surface convergence (near genesis area).
• High dewpoints pooled near front/genesis area.
• Surface Theta-E values very high along derecho
  track.
• Derecho often moves parallel to front with slight
  component toward warm sector.

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09z MSAS surface analysis

• East-west surface boundary
• Surface dewpoints in the mid 70s south of the
  front
• Cold pool over SW Missouri and NW Arkansas

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09z LAPS CAPE LI/CIN
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Progressive Derecho EnvironmentJohns et al. 1990

• B. Upper Pattern
• Anticyclonically curved flow near upper ridge
  axis.
• Weak shortwave trough located upstream.
• Warm advection present at 850 mb and 700 mb near
  genesis area with weaker advection downwind.
• 850 mb moisture very high and pooled just south
  of the bow echo track.
• Large dewpoint depressions can be present at 700
  and 500 mb.

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12z Eta Analysis 250 mb

• Upstream trough axis from the Great Lakes into
  Missouri
• Mid South located in right entrance region of
  Ohio Valley jet max
• Strong divergence across the Mid South
• Weak upper ridge axis across the Mid South

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06z Eta 3hr Forecast VT 09z 850mb

• Moisture pooling south of boundary

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Progressive Derecho EnvironmentJohns et al. 1990

• C. Thermodynamic and Vertical Wind Profile
• Long lived events associated with very unstable
  air mass.
• Average maximum CAPE roughly 2400 j/kg in genesis
  area.
• Greater instability downwind where average
  maximum CAPE is 3500-4000 j/kg.
• Extreme instability due to pooling of moisture
  near front.
• Winds at 850 and 700 mb show good veering near
  genesis area, and mainly speed shear parallel to
  the storm track.

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7/21/03 00z LZK sounding

• CAPE
• 6584 j/kg
• Lifted Index
• -13C
• 850500mb lapse rate
• 7.6 C/KM
• DCAPE
• 1992 j/kg!!!

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06z Eta VT 09Z Theta E
329 K

• Theta E difference
• 31K

360 K
MEM
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Radar Loop0848Z 1345Z
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0.5 Reflectivity - 1117Z

• Strong thunderstorms working southeast toward
  area overnight
• Reached area of unstable air just west of Memphis
• Storms quickly exploded

Supercell 3
RIJ
Supercell 2
RFD
Supercell 1
RFD
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Conceptual model of squall line with trailing
stratiform areaHouze et al. 1989
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1.5 Velocity - 1117Z

• Rear Inflow Jet 50-64 knots

• Rear Inflow Jet may be reaching gust front

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0.5 Reflectivity - 1132Z

• Cells merging just west of the river

RFDs intersecting
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0.5 Velocity (8 bit) - 1132Z
KNQA 88D

• 60 mph winds approaching river
• Winds are stronger since the WSR 88D measures a
  component of the actual wind
• 1900 ft AGL

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0.5 Reflectivity 1147Z
1147Z July 22, 2003
Pronounced Rear Inflow Notch (RIN)
Bow Apex
Outflow Boundary
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0.5 Reflectivity 1152Z
1152Z July 22, 2003
Continued pronounced Rear Inflow Notch (RIN)
Bow Apex
Outflow Boundary
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0.5 Velocity (8 bit) - 1157Z
100 mph

• Doppler measures 58 mph wind (component away from
  radar)
• Calculations (Cosine times measured wind) yield
  over 100 mph wind over East Memphis
• 800 ft agl

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Radar Loop1117Z 1214Z
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0.5 Velocity (8 bit) - 1226Z

• 109 mph at 1500 ft agl

• As bow echo moves away from radar we have a
  better view of the actual wind speeds

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Destruction at Dawn WMC - TV5
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Summary

• Bow echo moved through the Memphis Metropolitan
  Area during the early morning of July 22nd
• City of Memphis paralyzed
• Airport closed
• Over 750,000 people without power
• 75 of traffic signals not working
• Widespread effect on human activity ranks this as
  probably the most severe wind storm (non tornado)
  in recent Mid South history.

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Special Thanks

• James Duke, MIC - WFO Memphis
• Scott Cordero, WCM - WFO Memphis
• Gerry Rigdon, SOO - WFO Memphis
• Bob Rozumalski - COMET
• Mark Frazier, Forecaster WFO Memphis
• Kati Sommer, Forecaster WFO Memphis

The End