Instability is when the air spontaneously rises and it is warmer than the air around it at a given height. If you need more information about this concept look on page 317 of the Reader. One factor that helps to contribute to instability is the uneven heating of the ground. A southerly wind can also contribute to instability. This wind can increase the dew point, and when you increase the dew point you create a higher latent heat.
Unstable air is what helps to create thunderstorms .
If there is a greater dew point there is more water vapor. Water vapor plays a great role in instability. If there is more water vapor there are more thunderstorms. Evaporation occurs when water changes, for every gram there is a tremendous amount of cooling. It is associated with latent heat.