The mature air mass thunderstorm contains heavy rain, thunder, lightning, and produces wind gusts at the surface. Mature thunderstorm cloud with typical anvil shaped cloud. The mature thunderstorm 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.
Thunderstorms form from the equator to as far north as Alaska.
They occur most commonly in the tropics were convectional heating of moist surface air occurs year round. Many tropical locals over land experience over 100 thunderstorm days per year. Thunderstorm formation over tropical oceans is less frequent because these surface do not warm rapidly. Outside the tropics, thunderstorm formation is more seasonal occurring in those months where heating is most intense. Figure 5t-5 describes the annual average number of thunderstorm days across the United States.