Thunderstorm development requires an unstable atmosphere. The more unstable the atmosphere, the more violent the potential thunderstorms. For this reason, meteorologists carefully monitor the stability of the atmosphere. Last time, we went through a tabular method for assessing stability. Below is a list of three basic changes that tend to make the atmosphere more unstable. You should be able to understand why each of these would make the atmosphere more unstable.

1. Warm the air near the surface. Rising parcels which start out warmer have a better chance of becoming warmer than the surrounding environment as they are lifted.
2. Cool the air aloft (above the surface). Colder environmental conditions above the surface make it more likely that lifted surface parcels will be warmer than the surrounding environment.
3. Add more water vapor to the air near the surface. More water vapor in a rising parcel means that more latent heat will be released during cloud formation and increases the likelihood that the parcel will become warmer than the surrounding environment.