Thunderstorms form as warm, moist air rises. This upward movement of air can result from surface heating. Areas that are heated by sunlight transfer some of this energy to the air that is directly above. As the air warms, it becomes less dense and starts to rise.
Air can also rise due to the arrival of a cold front. Because cooler air is more dense than warmer air, cooler air “hugs” the ground and can act as a wedge. As it collides with the warmer air mass, it pushes the warm air skyward. The ascending air forms and fuels the towering clouds of a thunderstorm. A system such as this can spawn strong winds, lightning, heavy precipitation, and even tornadoes.
The upward movement of air acts like a conveyor belt. The atoms and molecules that make up the air are transported skyward, carrying energy into the thunderstorm-generating clouds in the atmosphere. Some of this energy is kinetic energy, exhibited by the increased movement of warm air up into the atmosphere. However, most of the energy that fuels thunderstorm formation is latent heat energy contained within the water vapor—water molecules in their gaseous state—in the rising air.
As water vapor rises into the atmosphere, it releases heat energy when it cools. As a result, the temperature of the water vapor drops. When the temperature of the air decreases to its
dew point—the temperature at which water vapor condenses into water—water droplets begin to accumulate on tiny particles of dust in the atmosphere, forming a cloud.
During this phase change, water vapor releases its substantial store of latent heat energy, fueling the thunderstorm. The additional energy allows the air to rise high into the troposphere. The storm cloud is continually fed with more energy from the updraft of warm, moist air that is rising into it. As air cools high in a thunderstorm, it also begins to descend in some places. These downdrafts can be accompanied by heavy rain and hail. The cycle of rising and descending air forms an atmospheric convection that strengthens the storm.
Eventually, the thunderstorm runs out of the energy it needs to maintain its forceful presence. With its fuel of water vapor transformed into downpours, little energy is left to power storm winds. Without updrafts, the system is further starved of rising and condensing vapor. As the remaining winds weaken, the thunderstorm dissipates