A few weeks ago there was a huge fire at an industrial complex in Bridgeport, northwest of Philadelphia. The winds that day were blowing steadily at around 20 mph from the north, helping to spread the fire and making fighting it all that much more difficult.

Fires can also create their own weather. For example, firefighters have sometimes reported encountering tornadoes of flames, especially in large wildfires like those that might strike forests in the western United States during the summer.

These fiery whirlwinds develop because of the huge temperature differences between the fire itself and the cooler surroundings. These temperature extremes create large pressure differences, and pressure differences create wind. So around a large fire, a maelstrom of swirling winds can blow strongly in a helter-skelter pattern, fanning flames, spreading sparks, and consuming new supplies of oxygen that feed the fire. In turn, these swirling winds sometimes spin up into tornadoes of fire, funnels of hot embers that are very, very dangerous to firefighters.