Make Your Own Thunderstorm
What you will need:
It's all about convection! The cold water sinks while the warmer red water rises, or stays higher than the blue. Convection is the action of warm air rising and cold air sinking. You probably guessed that the blue water represents a cold air mass and the red water represents the warm, unstable air mass. A thunderstorm is caused by unstable air and convection plays an important part. A body of warm air is forced to rise by an approaching cold front. Other things can cause warm air to rise, like a mountain slope.
A strong, persistent updraft of warm moist air is formed and lifted by the approaching cold front. Speeds in an updraft can be as fast as 90 miles per hour! The air cools as it rises, condenses, and forms cumulus clouds. When condensation occurs, heat is released and helps the thunderstorm grow.
At some point, condensation high in the cloud (now in the form of water droplets and ice) falls to the ground as rain. A cold downdraft forms as the rain falls.