A parcel of air lifted in the atmosphere expands and cools at a fixed rate — about \( 9.8\,^{\circ}\mathrm{C} \) per kilometre while unsaturated, and roughly \( 5\,^{\circ}\mathrm{C} \) per kilometre once condensation begins releasing latent heat. Stability is a comparison: if the surrounding air cools with height faster than the rising parcel does, the parcel stays warmer, stays buoyant, and keeps rising, and the atmosphere is unstable; if the surroundings cool more slowly, the parcel is quickly colder than its surroundings and sinks back, and the atmosphere is stable. Nothing about a fire changes this test — a fire simply supplies a very hot parcel. The consequence for fire is direct: an unstable atmosphere lets a fire's convection column grow tall and draw strong indrafts, while a stable one caps it and spreads the smoke sideways. The confusion this resolves is thinking stability describes the wind; it describes the atmosphere's willingness to let air rise. After this Concept you can decide from a temperature profile whether a fire's plume will grow or flatten.
Adiabatic processes change an air parcel's temperature through compression or expansion alone, without net energy exchange with the surroundings, in contrast to diabatic processes which involve direc…