Answer to Question 1
Thunderstorms form when warm, humid air rises in an unstable environment. Various mechanisms can trigger the upward air movement needed to create thunderstorm-producing cumulonimbus clouds.
Answer to Question 2
There are three stages in a thunderstorm's life: the cumulus stage, the mature stage, and the dissipating stage. The cumulus stage is the development stage, where there is only an updraft and no precipitation. As the storm develops, precipitation is produced in the upper parts of the cloud. Eventually, the rising air can no longer keep the growing droplets suspended in the cloud, and they begin to fall. As drier air from around the cloud is drawn in, this starts the downdraft and the mature stage. The mature stage is the height of the storm's intensity. During this stage, there is an updraft and a downdraft, precipitation, and severe weather. The top of the cloud has reached the stable region of the atmosphere and begins to take on an anvil shape. Eventually, the dissipating stage is reached, which is dominated by the downdraft. As the downdraft strengthens, it cuts off the updraft and stops the inflow of moist air. Deprived of humid air, the storm rains itself out.