They form when you get humid air that rises for whatever reason, condenses and forms clouds, and dumps precipitation and has strong enough updrafts and downdrafts to produce lightning. The really nasty ones form when you get a bunch of warm moist air on the ground, and then cool dry air slides in on top (this particular event is called a dry line).

This makes the atmosphere incredibly unstable since the warm air wants to go up really quickly. As it goes up and forms clouds, it creates an updraft that has to suck in more warm moist air from the ground to replace it. So the storm now feeds itself and continues to grow until it tops out at 30,000 feet and gets pushed around by the upper-level winds; which blow the top of the storm out in front of it to produce the classic anvil shape. Eventually the droplets of moisture get too big for the updrafts to hold them so they fall, creating downdrafts. Eventually the downdrafts tear the storm apart, but often not before it dumps baseball-sized hail and produces tornados if you're unlucky.

"Thunderstorms are one of the most common and most noticeable weather products of our atmosphere. They form worldwide, spit out deadly lightning, band together to form hurricanes, and can spin up the world's fastest winds inside tornadoes." (USA Today)

Also called an electric storm.

    Three stages to a thunderstorm:
  1. Cumulus Stage
    • Masses of moisture push upwards
  2. Anvil Stage (Mature Stage)
    • Rising air reaches hotter air above, can rise no more so spreads out creating anvil formation
    • Most rain occurs during this stage
  3. Dissipation Stage
    • No more updraft, no more moisture, slowly weak down drafts dissipate clouds.
    It can be said thunderstorms kill themselves out.

The typical thunderstorm lasts 30-60 minutes. During the storm the likelihood of lighting is higher at the beginning of the storm, and at the end. Since most of the rainfall is during the middle of the storm you need to keep in mind that when the rain stops you still need to be aware that lightning is likely. Cold fronts, drylines, or afternoon heating, which causes warm air to rise, can trigger thunderstorms. Three things are needed to create a thunderstorm, 1. Moisture, 2. Unstable Air, and 3. Lift. ”Thunderstorms begin when a parcel of warm, moist air begins to rise. As the air expands and cools, the water vapour within it condenses and forms a cloud (When air masses collide). If there is sufficient atmospheric instability, the heat released by condensation will keep the air inside the cloud warmer than the air surrounding it, enabling it to grow larger and higher. The power of the rising air, or updraft, keeps millions of water droplets in suspension until they become so heavy they fall as rain.” (Canadian Geographic) For a storm to be classified as a thunderstorm there must be existence of lightning. Lightning is needed to create thunder, and thus the thunderstorm. Not all thunderstorms have rain, there are such things as dry thunderstorms. They are a common occurrence across the western United States and a problem in starting wildfires.

Radars detect where rain and hail are located in the storm. Doppler radars detect wind direction within and near the storm. Some features of thunderstorms, such as the anvil that spreads out at the top of the storm, can be seen from satellites. Why would the sky appear orange after a thunderstorm? "Most thunderstorms occur in the late afternoon. By this time of day, the sun is setting. The orange hue is caused by the same reason sunsets vary from yellow to orange to red: shorter wavelengths of light (blue) are scattered quickly, leaving only the yellow-orange-red end of the spectrum." (NSSL) Which is enhanced by the humidity in the air from the thunderstorm.

    Four classifications
  • Single cell
  • Multicell
    • Group of cells at different stages.
    • ”The cloud becomes divided into updraft and downdraft regions separated by a gust front.
      • The gust front may extend for several miles ahead of the storm, bringing with it increases in wind speed and atmospheric pressure, decreases in temperature, and shifts in wind direction.” (Wikipedia)
  • Squall line
    • Organized line of multicells.
    • Tendency to be hundreds of miles long.
  • Supercell
    • Forms when the wind speed and direction vary with height, or wind shear, separates downdrafts from updrafts.
    • Most tornados are caused by this classification.

To be declared as a severe thunderstorm, it must have either winds 92.5 kilometers/hour (57.5 mph) or greater, 1.9 centimeter (¾ in) or larger hail, or funnel clouds or tornadoes. “Out of the estimated 100,000 thunderstorms that occur in the U.S. each year, only 10 percent become severe.” (USA Today)

    For your safety, when outdoors during a thunderstorm:
  • Stay low.
  • If possible, find shelter in a building.
  • Keep away from trees, tall objects, metal objects and water.
  • Boaters and swimmer should get to land as a soon as possible.
  • If you're in a group caught outside, spread out.
  • If you begin to feel your hair stand on end, this indicates lightning is about to strike. You should drop to your knees and bend forward placing your hands on your knees and crouch down. Do not lie flat on the ground, this will only make you a larger target.
  • Safety tips from (USA Today)

Thunderstorm is also a former band.
"The Band's roots date back to the earliest 90s, when Fabio "Thunder" Bellan starts a Classic Heavy Metal Band with a touch of Doom, and calls it "Thunderstorm." Afterwards the Band releases two demotapes ("Thunderstorm" and "Force of Evil"), which despite of their sourness, show a resolute and articulated sound. In 1998, after several changes of Line-up, the Band splits up due to musical incompatibility." (Band Homepage)

Thun"der*storm` (?), n.

A storm accompanied with lightning and thunder.


© Webster 1913.

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