Thunderstorms & Tornadoes
(1). Unequal warming of the surface of the Earth.
(2). Orographic lifting due to topographic obstruction of air flow.
(3). Dynamic lifting because of the presence of a frontal zone.
Sequence of events as the parcel of air rises:
air cools due to adiabatic expansion
at a certain altitude the dew point is reached
when the dew point is reached the relative humidity equals 100% and the air is saturated
condensation begins resulting in latent heat being changed into sensible heat, warming the air and making it more unstable
a cumulus cloud begins to form
For the cumulus cloud to form into a thunderstorm, continued uplift must occur in an unstable atmosphere.
With the vertical extension of the air parcel, the cumulus cloud grows into a cumulonimbus cloud. Cumulonimbus clouds can reach heights of 20 kilometers above the Earth's surface.
Severe weather associated with some these clouds includes hail, strong winds, thunder, lightning, intense rain, and tornadoes.
Generally, two types of thunderstorms are common:
1) Air mass thunderstorms which occur in the mid-latitudes in summer and at the equator all year long.
2) Thunderstorms associated with mid-latitude cyclone cold fronts or dry lines. This type of thunderstorm often has severe weather associated with it.
The mature thunderstorm (Stage 3) begins to decrease in intensity and enters the dissipating stage after about half an hour. Air currents within the convective storm are now mainly downdrafts as the supply of warm moist air from the lower atmosphere is depleted. Within about 1 hour, the storm is finished and precipitation has stopped.
Exploding Air: Any time there is an electrical current, there is also heat associated with the current. Since there is an enormous amount of current in a lightning strike, there is also an enormous amount of heat. In fact, a bolt of lightning is hotter than the surface of the sun. This heat is the actual cause of the brilliant white-blue flash that we see.
When a leader and a streamer meet and the current flows (the strike), the air around the strike becomes extremely hot. So hot that it actually explodes because the heat causes the air to expand so rapidly. The explosion is soon followed by what we all know as thunder.
Thunder is the shockwave radiating away from the strike path. When the air heats up, it expands rapidly, creating a compression wave that propagates through the surrounding air. This compression wave manifests itself in the form of a sound wave. That does not mean that thunder is harmless. On the contrary, if you are close enough, you can feel the shockwave as it shakes the surroundings. Keep in mind that when a nuclear explosion occurs, typically the most destruction is caused by the energy of the rapidly moving shockwave. In fact, the shockwave that produces the thunder from a lightning strike can most certainly damage structures and people. This danger is more prominent when you are close to the strike, because the shockwave is stronger there and will dampen (decrease) with distance. Physics teaches us that sound travels much slower than light, so we see the flash before we hear the thunder. In air, sound travels roughly 1 mile every 4.5 seconds. Light travels at a blazing 186,000 miles (299,000 kilometers) per second.