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Section 8.3 Tornados

NOAA Jetstream:

Most tornados form underneath supercell thunderstorms (most supercells do not form tornadoes, but most tornadoes form from supercells)

  • The cloud base underneath the updraft on the rear side of the thunderstorm may lower, forming a rotating wall cloud

  • A rapidly rotating column of air much smaller than the mesocyclone may protrude beneath the wall cloud

  • 200-250 mbar pressure drop

  • As water vapor condenses in the air rushing up into this column, a funnel cloud may form and reach the ground, becoming a tornado air rushes up into low pressure core of mesocylone expansion, cooling, and cloud formation descending air in core (may reach ground)

formation & organization

  • descending air in rear-flank downdraft wraps around mesocyclone

  • rain/hail in RFD can produce hook echo

  • becomes focused on surface area of lower pressure

  • formation of funnel cloud and debris: funnel is rapid condensation of water due to adiabatic cooling


  • rapid inflow of warm, moist air into vortex

  • peak strength and size (usually 100-200 meters in size; but up to ~1 mile in diameter)

  • RFD begins wrapping around vortex


  • RFD complete wraps around tornado

  • intensity decreases, tornado tilts with height

  • drawn into thin, rope-like structure

Radar Signatures

  • hook echo

  • TDS (tornado debris signature)

  • Doppler rotation —> vortex signature

  • these advances are creating increasing lead times for advanced warning

Tornado Strength

  • Wind estimation based on observations of tornado damage

  • Enhanced Fujita (EF) scale ranges from 0 to 5, with 5 the most damage

    • The scale uses 28 damage indicators, like schools, barns, and vegetation; the damage to each helps place the tornado on the scale

    • higher EF number, the more severe the tornado’s wind and damage

  • Some of the most severe tornadoes are multiple vortex tornadoes