A strong fire plume carries hot, moisture-laden air upward; if it rises far enough for that moisture to condense, latent heat release adds buoyancy the fire did not have to supply, and the column can grow into a full thunderstorm — a pyrocumulonimbus, or pyroCb. These storms have been observed to reach the lower stratosphere, and they close a feedback loop that makes fire behaviour far harder to predict: they generate their own lightning, igniting new fires ahead of the front; they produce strong, erratic downdrafts and outflow winds at the surface; and their inflow strengthens the parent fire. They require a deep unstable layer aloft, enough moisture, and a very large heat release, which is why they accompany only the most intense fires. The confusion this resolves is treating a fire's smoke column and a thunderstorm as separate things. After this Concept you can recognise the conditions under which a fire stops being a passive plume and starts making its own weather.
In fire weather science, a firestorm is a self-sustaining convective phenomenon that arises when a wildfire's heat and combustion-produced water vapor create the same rising-hot-air/cold-air-aloft dy…