To start making a thunderstorm, you first need convection. Convection is the idea that in different mediums, like air or water, heat rises and displaces colder temperatures. Convection works with the water in the ocean, and the air in the atmosphere. 

Convection starts with the sun heating the surface of the earth, raising the temperature of the ground. The ground radiates heat, and warms the air above it. The heated air becomes lighter and rises into the atmosphere. This pocket of rising warm air is called an updraft. 

When updrafts rise, they carry water vapor with them. As an updraft rises through the atmosphere, it reaches a point where the air temperature is low enough to water to condense. The water vapor in the updraft begins to condense and accumulate, creating a cumulus cloud. As long as the updraft continues to be strong and moisture is plentiful, the cloud will grow. The condensed water and ice in the cloud will be held aloft by the continuing updraft. 

As more moisture is added to the cloud and condenses, the water droplets grow and become too big for the updraft to hold aloft. The droplets begin to fall through the cloud toward the ground. As they fall, the precipitation cools the air around it. Soon, portions of the air are too cool to stay aloft, and the cold air falls with the rain and ice. This is the creation of a downdraft. 

The downdraft moves against the updraft in the cloud. As more precipitation falls from the cloud, the downdraft is strengthened and the updraft weakens. The downdraft exits at the base of the cloud and spreads out along the ground, in advance of the actual thunderstorm. The arc-like leading edge of the downdraft is called a gust front, and resembles a mini cold front, because the downdraft air is cool. 

As more and more precipitation falls, the downdraft strengthens and spreads throughout the cloud. Subsidence takes place, replacing the warm air of the updraft with the cooler downdraft. With the updraft replaced, the thunderstorm loses its power and stops, and eventually the cloud drifts apart. 

The graph above shows the temperature of the atmosphere in relation to height. By going just a small distance into the atmosphere, the temperature is low enough for water to condense, an important step in the creation of thunderstorms.

Visit the NOAA Aeronomy Laboratory to find out more about the atmosphere: www.al.noaa.gov