Environmental And Radar Characteristics Of A Destructive Downburst

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Environmental And Radar Characteristics Of A
Destructive Downburst
December 3rd 2001
James Taylor and Rob Webb N.S.W Severe
Weather June 2002
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December 3 2001

• Damage
• Mechanisms Which Enhance Downbursts
• Pre-storm Environment
• Radar Characteristics
• Conclusion

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Damage

• Two people killed
• Damage at Richmond RAAF Base, Control Tower
  windows blown out, trees came down and planes
  were damaged
• Roofs lifted and buildings damaged by fallen
  trees particularly in northern subs
• SES had 5800 calls

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Synoptic Situation 1000am
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Mechanisms Which Cause Severe Downbursts

• Entrainment of dry air in the mid-levels and
  below cloud base
• Cooling through latent heat of fusion and latent
  heat of evaporation - negative buoyancy, large
  DMAPE
• Precipitation drag
• Vertical pressure gradients
• Strong mid level winds - momentum transfer

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Pre-storm Environment
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Convective Gusts
Calculated max. wind gust from
96 knots
Calculated convective Gust strength 106 knots
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Radar Characteristics

• Descending Core - precipitation drag
• Large reflectivity - Large amount of rain/hail
• Mid Level dry notch - entrainment, -ve buoyancy

Doppler Radar Characteristics

• Divergence as downburst hits the ground
• Widespread radial convergence at highest
  reflectivity area