AS

Types of Thunderstorms

Air-Mass Thunderstorm

  • most common type
    • occur locally
    • last short lengths of time
  • cumulus clouds form when warm air mass rises high enough that it cools to its dew point and water vapor condenses
    • energy source due to heat released through condensation
  • clouds continue to build and this leads to cumulonimbus clouds up to 12 miles high
  • precipitation occurs when mass of water/ice is too heavy for updrafts to support that leads to falling rain that creates downdrafts
  • self-extinguishing as precipitation falls into core of updraft; drags down cool air and cool air created as precipitation evaporates (uses energy)
  • cool air reaches surface and expands, cutting off supply of warm air to storm

Severe Thunderstorm

  • must meet one of the 3 conditions to be considered severe:

    1. wind > 50 knots (58 mph)
    2. hail 1 inch or larger in diameter
    3. tornado

  • two air masses collide

  • advancing front of cold air lifts the warm air

  • numerous thunderclouds generated along 60-600 mile long zone

  • large area with thunderstorms is where updrafts/downdrafts of storms occur simultaneously and reinforce each other

Supercell Thunderstorm

  • particularly violent type of severe thunderstorm
  • huge updraft of air
  • move laterally
  • pick up fuel (warm, moist air) in front and dump exhaust (cool, dry air) behind
  • get very big (12-30 miles) and can last several hours
  • rotation of the updraft creates a vortex
    • many of the most powerful tornadoes develop from this

Thunderstorms in the US

  • not equally distributed
  • mostly affect the central and southern US
  • most occur in the spring and early summer when warm, moist air from the Gulf of Mexico moves northward
    • meets cold air masses, overrides them, and lifts warm air upwards
  • also occur in mountainous regions where warm, moist air rises