A firestorm is a conflagration which attains such intensity that it creates and sustains its own wind system. It is most commonly a natural phenomenon, created during some of the largest bushfires, forest fires, and wildfires. The Great Peshtigo Fire and the Ash Wednesday fires are two examples of a firestorm. Firestorms can also be deliberate effects of targeted explosives such as occurred as a result of the aerial bombings of Dresden, Hamburg, Tokyo and the atomic bombing of Hiroshima during World War II.

Source: Wikipedia