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