What is a Firestorms??

fire·storm n. -- A fire of great size and intensity that generates and is fed by strong inrushing winds from all sides: the firestorm that leveled Hiroshima after the atomic blast.

Wind probably has the biggest impact on a wildfire's behavior. It also the most unpredictable factor. Winds supply the fire with additional oxygen, further dry potential fuel and push the fire across the land at a faster rate.

Dr. Terry Clark, senior scientist at the National Center for Atmospheric Research, has developed a computer model that shows how winds move on a small scale. Since 1991, he's been converting that model to include wildfire characteristics, such as fuel and heat exchange between fires and the atmosphere.

"We look at what's called coupled fire atmosphere dynamics, where the fire and the atmosphere interact with each other," Clark said. "We've been looking at how fires interact with the environment and getting some of the characteristics of fire spread and fire behavior, through the modeling that we've been doing."

Clark's research has found that not only does wind affect how the fire develops, but that fires themselves can develop wind patterns. When the fire creates its own weather patterns, they can feed back into how the fire spreads. Large, violent wildfires can generate winds, called fire whirls. Fire whirls, which are like tornadoes, result from the vortices created by the fire's heat. When these vortices are tilted from horizontal to vertical, you get fire whirls. Fire whirls have been known to hurl flaming logs and burning debris over considerable distances.

"There's another way that you can tilt the vorticity. That is it can be titled without breaking into fire whirls, and basically be burst forward into what's called hairpin vortices or forward bursts," Clark said. "These are quite common in crown fires [fires at the top of trees], and so you see fires licking up hill sides." Forward bursts can be 20 meters (66 feet) wide and shoot out 100 meters (328 feet) at a speed of 100 mph (161 kph). These bursts leave a scorched region and lead to fire spread.

The stronger the wind blows, the faster the fire spreads. The fire generates winds of its own that are as many as 10 times faster than the ambient wind. It can even throw embers into the air and create additional fires, an occurrence called spotting. Wind can also change the direction of the fire, and gusts can raise the fire into the trees, creating a crown fire.