The Easter Weekend Tornadoes of April 3, 1999'

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The Easter Weekend Tornadoes of April 3, 1999.

• Michael Berry, Senior Forecaster, National
  Weather Service in Shreveport, Louisiana.

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A Brief History of the National Weather Service
Shreveport Since the Doppler Era.

• NWS Shreveports Doppler Radar was first
  commissioned in
• 1995.
• We have forecast and warning responsibility
  for portions of
• four different states which encompasses
  34,471 square miles.

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NWS Shreveports County Warning Area

• NWS Shreveports County Warning Area consists of
  extreme Southeast
• Oklahoma, Southwest Arkansas, Northeast and East
  Central Texas as
• as well as Northwest and North Central Louisiana.

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Tornado History for NWS Shreveports County
Warning Area since 1995.

• 235 Tornadoes 1995 - 2005
• F0 (40-72 mph) 66
• F1 (73-112 mph) 88
• F2 (113-157 mph) 57
• F3 (158-206 mph) 23
• F4 (207-260 mph) 1
• F5 (261-318 mph) 0

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Trivia Question Who is this Man???

• Theodore Fujita (1920-1998).
• Groundbreaking research into tornadogenesis and
  the damage that resulted from these storms.
• Responsible for our Fujita Tornado Scale (Fujita
  Scale), a system of classifying tornado intensity
  based on damage to structures or vegetation.

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The Fujita Scale

• Pie chart reveals that a vast majority of
  tornadoes are weak or only do damage attributed
  to that of a weak (F0-F1) tornado.
• Only a small percentage of tornadoes can be
  correctly classified as violent (F4-F5).

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The Fujita Scale

• While only 1 of tornadoes are rated as violent
  (F4-F5) in intensity, these tornadoes result in a
  much higher percentage of deaths across the
  country (67).

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How Does Doppler Radar Work ?

• The radar transmitter sends out a radar pulse at
  different elevation
• slices. The pulse comes into contact with a
  precipitation target.
• The pulse gets reflected back towards the radar
  receiver. The received
• signal goes through numerous algorithms and
  the picture we get back
• is in the form of

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• Reflectivity Image Velocity
  Image

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Dynamics of April 3, 1999

• Conditions at the surface.
• Conditions above the surface on a Synoptic
• and Mesoscale.
• Dissect each individual storm observing
• not only Reflectivity (Z) but Storm Relative
• Velocity (SRM) as well.

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Atmospheric Conditions on April the morning of
April 3, 1999.

• 250mb (35,000ft) Jet Stream winds indicate
• 1) Upper level Jet Stream axis
  across the Southern Rockies.
• 2) Jet Streak of 70kts across NE Texas and
  NW Louisiana.
• 3) Favorable region of Upper Level
  Divergence (Necessary to
• provide lift in the atmosphere).

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Atmospheric Conditions Continued

• 500mb (19,000ft) Heights/Vorticity Map
  indicates
• 1) Deep trough of low pressure
  across the four-corners region.
• 2) Strong ridge of high pressure
  across the eastern Conus.
• 3) Darker areas embedded in the
  trough represent areas of
• vorticity (againfavorable
  areas for lift).

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Atmospheric Conditions Continued

• 700mb (10,000ft) Upward Verticle Motion Field
  indicates
• 1) Dotted line represents area
  of best upward motion.
• 2) Solid lines represent
  downward verticle motion.
• 3) Upward motion coincides
  well with divergence aloft
• present at 250mb
  (35,000ft).

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Atmospheric Conditions Continued

• 850mb (5,000ft) Wind field and thermal field
  reveals
• 1) Low level jet of 45kts evident
  across Ne Tx, Nw La.
• 2) Thermal axis extends from
  Central through Ne Tx, Nw La, Sw Ar.
• 3) Jet hints that strong shear in
  present in the lower atmosphere and
• the Thermal axis is indicative
  of a boundary at that elevation.

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Surface Analysis of April 3rd (800am cst)

• Unstable environment already present in the
  morning (7 hrs before tornadic thunderstorm
  development.)
• Morning temperatures in the 70s, with dewpoint
  temperatures in the upper 60s. (Abundant low
  level moisture already present).
• Surface cold front to our west.

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Surface Analysis of April 3rd (1200pm cst)

• South winds increased dramatically (15 to 20 mph
  sustained with gusts to 25 mph.)
• Temperatures warming into the 80s, dewpoints
  rising into the 70s.
• Cold front remains stationary but a prefrontal
  trough has developed across Northeast Texas.
  (Storms will develop on this boundary.)

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So What Does All This Mean???

• Deep trough in association with strong upper jet
  streak will provide the lift necessary for
  thunderstorm development.
• Lifting mechanism needed to initiate storm
  development will be in the form of a prefrontal
  trough.
• Atmosphere is becoming more unstable as the day
  continues to warm and more moisture is supplied.
• Winds are sufficient enough in the middle and
  lower levels of the atmosphere to produce
  supercells.
• Winds are veering with height in the lowest few
  thousand feet while surface winds are showing a
  tendency to back ahead of the prefrontal trough
  (this is called shearthe necessary ingredient
  for tornadic supercells.)
• As a resultconditions are primed for a possible
  significant tornado outbreak across the Arklatex.

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Storm 1 (Shelby County/Desoto Parish Tornado)
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Shelby County/Desoto Parish Tornado Statistics

• NWS Storm Survey rated the tornado as an F3
  (158-206 mph winds).
• Path Length 5.4 miles long. (2.8 miles in
  Shelby County and 2.6 miles in Desoto Parish).
• Path Width Ranged from 50 yards wide across
  Shelby County to 150 yards wide in Desoto Parish.
• No Deaths, 1 injury.
• Damage consisted of numerous homes and buildings
  with moderate to severe damage. Some wood frame
  homes lost all exterior walls with roofs
  partially or completely removed. Interior walls
  still standing.

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Storm 2 (Caddo/Bossier Parish Tornado)
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Benton Tornado Video
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Caddo/Bossier Parish Tornado Statistics

• NWS Storm Survey rated the tornado as an F4
  (206-260 mph winds).
• Path Length 19.3 miles long. (6.7 miles in
  Caddo Parish and 12.6 miles in Bossier Parish).
• Path Width Ranged from 150 to 200 yards wide.
• 7 Deaths, 112 injuries.
• Caddo Parish Damage Tornado first touched down
  over Cross Lake and moved northeast. A total of
  66 structures suffered moderate to significant
  damage. A steel framed hardware store was
  leveled.
• Bossier Parish Damage Tornado crossed the Red
  River and moved into the town of Benton. Some
  389 structures suffered moderate to significant
  damage. Brick homes were leveled with no
  exterior walls left standing. Most if not all
  interior walls of homes were leveled. One brick
  home was totally missing with only the slab
  remaining.

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Storm 3 (Claiborne Parish Tornado)
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Claiborne Parish Tornado Statistics

• NWS Storm Survey rated the tornado as an F3
  (158-206 mph winds).
• Path Length 23 miles long. (8 mile separation
  as the storm appeared to skip across Lake
  Claiborne).
• Path Width Ranged from 100 to 150 yards wide.
• No Deaths, No injuries.
• About 25 homes suffered moderate to major damage.
  Two mobile homes were completely destroyed and
  witnesses observed two automobiles levitating and
  rolled back to the ground. While the storm was
  over Lake Claibornewitnesses observed the
  tornado lift back into the wall cloud before
  dropping once again on the northeast side of the
  lake.

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Locally Derived Tornado Nomograms
Caddo/Bossier Tornado Max Shear 278 at 10nm
Shelby/Desoto Tornado Max Shear 51 at 33 nm
Claiborne Tornado Max Shear 36 at 41 nm
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Lessons Learned???

• SAME NWR Radio After buying your radioyou must
  program your county, parish or independent city
  or marine area into the radio.
• Your NWR will then alert you only of weather and
  other emergencies for the county(s)/ area(s)
  programmed.
• NWR receivers without the SAME capability alert
  for emergencies anywhere within the coverage area
  of the NWR transmitter, typically several
  counties, even though the emergency could be well
  away from the listener.

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• THE END
• But then againstorm preparedness never ends!