The Earth’s atmosphere is a mixture of gases, dust and water vapor. The atmosphere is divided into layers based on temperature changes. The lowest layer is called the troposphere, it is where weather occurs. The temperature and pressure decreases as the altitude increases.
Warm moist air rises creating a low pressure area. The raising air cools until it reaches the Dew Point (100% R.H.) Warm air weighs less than cold air, moist air weighs less than dry air.
Thunderstorms have areas of strong updrafts and strong downdrafts. Hail is formed when the tops of the large thunderhead clouds are below freezing. The hail falls, gets coated with water, is caught in the updraft and is refrozen when it reaches the top.