Thunderstorms, or the formation of one has many variables. It can be very hot, or you may see dark clouds. It's nothing to be afraid of. It's a natural cause that may accompany a few bolts of lightning. To look up more about thunderstorms, check out your local library.
Rain is a different type of weather.
Sometimes there is light, brief showers, and sometimes hurricanes or monsoons could occur. Rain is formed by water from the ground. Thus, you may experience rain. Plants is the answer. Well, really, to plants, that's what rain is like to them.