Convection in the atmosphere is complicated by two important factors. The pressure of the atmosphere decreases with increasing altitude. Convection is halted. In this condition the atmosphere is said to be stable . The atmosphere contains water vapour.
Water vapour contains an enormous amount of latent heat.
When humid air rises it expands and cools. When the air has cooled enough, clouds form and an enormous amount of latent heat is released through condensation . If the surrounding air is still cooler, the added heat causes further expansion of the air and convection accelerates. The atmosphere in this condition is said to be unstable . Extreme instability leads to runaway convection causing severe thunderstorms and possibly even tornados.