THUNDERSTORMS

1
THUNDERSTORMS

• FAVORABLE CONDITIONS
• UNSTABLE AIR
• INITIAL UPDRAFT
• HIGH MOISTURE CONTENT OF THE AIR
• LATENT HEAT RELEASED BY WATER VAPOR CONDENSATION
  INCREASES BUOYANCY OF RISING AIR COLUMNS AND
  MAKES THEM SELF-SUSTAINING

2
THUNDERSTORMS

• GREATEST DANGER IS FROM THE VERTICAL CURRENTS
  WHICH CAN CAUSE AIRCRAFT DISINTEGRATION
• THREE STAGES OF LIFE CYCLE
• CUMULUS
• MATURE
• DISSIPATING

3
THUNDERSTORMS

• SEVERITY GOVERNED BY MAKE-UP OF THE MATURE STAGE
• UPDRAFT MAY EXTEND FROM EARTH SURFACE TO SEVERAL
  THOUSAND FEET ABOVE VISIBLE CLOUD TOPS
• IN CUMULUS STAGE, TINY CLOUD DROPLETS GROW INTO
  RAIN DROPS AS CLOUD BUILDS UPWARD
• WHEN DROPLETS REACH SIZE THAT CANNOT BE SUPPORTED
  BY UPDRAFT, THEY FALL

4
THUNDERSTORMS

• MATURE STAGE STARTS WITH FALLING DROPLETS
• IN LIMITED STATE T-STORM, MATURE STAGE SELF
  DESTRUCTS WITH UPDRAFT UNABLE TO SUPPORT RAIN
  DROPS, AND PRECIPITATION FALLING THROUGH UPDRAFT,
  AND DOWNDRAFT DEVELOPING
• IF UPDRAFT AND DOWNDRAFT REMAIN BALANCED, GET
  STEADY STATE T-STORM

5
THUNDERSTORMS

• STEADY-STATE T-STORM HAS EXTREME TURBULENCE AND
  POSSIBLE LARGE HAIL
• GOOD INDICATOR OF STEADY-STATE STORM IS SURFACE
  TEMP AND DEWPOINT (IF DEWPOINT 50 F OR MORE, WITH
  30 F SPREAD BETWEEN TEMP AND DEWPOINT, SEVERE)
• LIMITED STATE T-STORM MAY LAST 20 MINS TO AN
  HOUR
• STEADY-STATE MAY LAST 24 HOURS AND TRAVEL 1000
  MILES

6
THUNDERSTORMS

• PILOT ACTIONS
• AVOID T-STORMS
• DO NOT FLY BELOW - DESTRUCTIVE SHEAR TURBULENCE
  POSSIBLE
• AVOID CELLS BY 20 MILES - HAIL AND VIOLENT
  TURBULENCE POSSIBLE
• REDUCE AIRSPEED TO VA IN T-STORM VICINITY
• MAINTAIN STRAIGHT AND LEVEL ATTITUDE ON HEADING
  TO MINIMIZE TIME IN STORM AREA - DONT ATTEMPT TO
  HOLD ALTITUDE IN VERTICAL DRAFTS

7
THUNDERSTORMS

• THUNDERSTORM CONDITION 2
• CONDITIONS FAVORABLE FOR T-STORMS WITHIN 40 NM OF
  STATION AND/OR WITHIN 6 HOURS
• THUNDERSTORM CONDITION 1A
• T-STORMS PRESENTLY WITHIN 40 NM AND EXPECTED TO
  AFFECT STATION
• THUNDERSTORM CONDITION 1
• T-STORMS IMMINENT AND WITHIN 10 NM
• CONDITION 1 - REFUELING AIRCRAFT PROHIBITED
• CONDITION 2 - REFUELING PERMITTED