The Hallam, Nebraska Tornado May 22, 2004

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The Hallam, Nebraska TornadoMay 22, 2004

• Brian E. Smith
• NOAAs National Weather Service
• Omaha/Valley, NE

The views expressed are those of the author and
do notnecessarily represent those of the
National Weather Service
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Day 1 Convective Outlook issued 1135 AM
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Crude Surface Chart at 00Z
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00Z Soundings from OAX and TOP
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22Z Satellite Imagery
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Surface Based Cape and CIN at 22Z
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0-3KM Storm Relative Helicity at 22Z
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3KM Energy Helicity Index at 00Z
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Lincoln
Bennet
Hallam
Daykin
Beatrice
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The Hallam Tornado

• The storm did not look like a tornado to spotters
  and chasers. The fact that the cloud base was
  very low, the tornado circulation was very wide,
  along with the tornado being rain-wrapped at
  times, and darkness setting in made the storm
  extremely difficult to identify.

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54 miles long, 2.5 miles wideF4
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Radar at 0004Z
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May 22, 2004A date that was unforgettable
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May 22, 2004A date that was unforgettable
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It does not always look like a tornado!
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833 PM, May 22, 2004
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Radar at 23Z
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833 PM, May 22, 2004
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It does not always look like a tornado!
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Damage in Hallam
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Aerial Photo over Hallam
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Derailed Freight Train in Hallam
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Damage at the Norris School
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MORE PHOTOS OF THE NORRIS SCHOOL
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F-4 Damage South of Hallam
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Bottom Plate stayed bolted down. But studs that
were straight nailed in lifted off.
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What is damage from mesocyclone or tornado?

• Large rain-wrapped tornadoes with low cloud
  bases, it may be difficult to discern what is a
  tornado.
• Reports from Hallam prior to the tornado
  striking, indicated only seeing a large rain
  shaft. Spotters should be wary of rain shafts in
  the mesocyclone area of HP Supercells. Radar
  information coordinated with spotter reports are
  important.

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What Worked For This Event?

• The National Weather Service was well aware that
  severe weather was possible, and accurate severe
  weather outlooks were issued appropriately.
• A Conference Call was held prior to the event, to
  alert Emergency Managers and Media of a
  high-impact event.
• The first tornado watch was issued at 345 PM,
  valid through 11 PM. This was a long-lived event
  that began 600 PM and continued through
  Midnight.
• No missed events occurred. Average lead time in
  Saline county was 17 minutes. Average lead time
  in Gage and Lancaster counties averaged 20 to 40
  minutes.
• A new Severe Weather Product (SVR, TOR, SVS, LSR)
  was issued approximately once every 3.8 minutes
  during the event.
• The event was very well handled, despite a staff
  shortage at the WFO.

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Conclusions

• The Hallam storm was a very complex tornado
  associated with the HP or hybrid Supercell.
  Multiple vortices and satellite vortices added to
  the complexity of the storm structure.
• The question of whether this tornado was the
  widest is questionable. Strong (gtF2) damage was
  around 2 ½ miles wide at one point. But this was
  based only on a ground survey.
• A detailed aerial survey would have provided more
  concise answers to the structure and width of the
  storm.