Excerpt: Storm Chaser Reed Timmer's 'Into the Storm'

Oct. 14, 2010— -- When a major storm strikes, most people have the good sense to either hunker down or get out of the way. Storm chasers, however, are a special breed. They run right for it.

Reed Timmer, one of the stars of the hit Discovery Channel show "Storm Chasers," details his adventures around some of the world's strongest storms.

Read an excerpt from the book below, and head to the "GMA" Library to find more good reads.

The dream starts with a breeze. When I envision the complex creation of the most violent and mysterious weather phenomenon of all—a three-hundred-mile-per-hour, landscape-churning, damage-scale-topping tornado—it starts with a soothing breeze.

Here in central Oklahoma, where I really do live, and where tornadoes rated the maximum F5 on mete-orology's Fujita Scale truly have gouged the earth time and time again, the breeze comes out of the south. The air is sultry—moist and warm. When it reaches your skin, it's as thick as lotion, and it makes you feel like you've been transported somewhere exotic. You almost have. The breeze originates in the Gulf of Mex-ico, where it once washed over beachgoers.

In my mind, I watch how this special air flows—meteorologists call this movement the low-level jet—as if it were a river, a thousand feet in the sky, extending halfway across the continent to the Great Plains. When the tropical air reaches the likes of Texas, Oklahoma, Nebraska, or Kansas, something curious happens. And the air is no longer a quiet, soothing breeze.

Near the earth's surface, moist air collides with different kinds of air coming from different directions. Hot, dry air from the American Southwest and northern Mexico. Cold air from the north, blown southward across Canada, all the way from the Arctic. Such a convergence doesn't happen everywhere, but in central Oklahoma it's hardly a freak event. The Great Plains—which weather nuts like me call Tornado Alley—is a rare, natural intersecting point for all this wind. About 90 percent of all tornadoes reported annually in the United States—some eight hundred or more per year—touch down in Tornado Alley.

In the birth of my envisioned F5, all of that clashing air follows a meteorological script. The hot, dry air in-jects the atmosphere with heat that serves as a springboard for the now warm, moist air to rise. As kids, we were taught that hot air rises—hot air molecules agitate more than cold air molecules, and, needing lots of room to move, the hot air expands upward. When an F5 forms over Tornado Alley, this ascension is violent, sometimes moving at over one hundred miles per hour. The surrounding cold air only helps matters. Cold air forces neighboring hot air to rise faster.

Then, approximately a mile above the ground, the moisture in the rising air condenses into a mist. This is the meteorological equivalent of a shark fin popping out of the ocean water. It marks the beginnings of a storm cloud. It's the first visible sign of danger.

Usually the rising air in a cloud quickly cools as it ascends, and the cloud stops moving up. But not dur-ing the formation of an F5. The rising air—the updraft—won't die. Condensation continues, and the traces of ascending mist accumulate, not unlike the way a snowball gathers more snow as it rolls downhill. But in the case of an F5, the "snowball" is climbing toward the heavens. On a humid spring day, folks in Tornado Alley can turn their backs on the sky for just minutes, to mow a lawn or wash a car. When they look up again, what was a cloud-free sky before has become blemished—more like dominated—by a lone, sunlit, bright white, ominous cloud.

The crisp cloud in my mind rapidly grows from a height of hundreds to thousands to tens of thousands of feet, blasting through the troposphere and into the stratosphere until it's thirteen miles tall. This is a cu-mulonimbus cloud, and in its most radical, towering form people say that it looks like the mushroom cloud that's associated with a nuclear explosion. Considering what an F5 tornado can do to both property and people, the metaphor isn't too far-fetched.

According to the Fujita Scale upon which the "F5" classification is based, such a tornado can flatten homes, turn cars into airborne missiles, and debark trees. The Fujita Scale is a widely accepted "damage scale" for categorizing tornadoes that's based on the havoc they wreak, and "F5" is used only to identify the most destructive rotating winds—those that spin anywhere from an estimated 261 to 318 miles per hour. Created by University of Chicago meteorologist Tetsuya "Ted" Fujita in 1971, the scale's other five catego-ries also use damage characteristics and estimated speeds to classify every other tornado: F0 (under 73 miles per hour); F1 (73 to 112 miles per hour); F2 (113 to 157 miles per hour); F3 (158 to 206 miles per hour); and F4 (207 to 260 miles per hour). In 2007, the "F-scale" was supplanted by a slightly modified "En-hanced Fujita Scale," or "EF-scale" (for consistency I've stuck with the F-scale, which was in use for most of my early days of storm chasing, throughout this book). Whichever scale you use, to suggest "F5" is to suggest almost unfathomable power.