Within a short time, the frigid outflow marks the beginning of the end of the storm. Lungs can’t inhale and exhale simultaneously. Without the energy source coming from the updraft, the storm devolves into a downpour of wind and rain and soon expires. Byers summed up the progression in a reliable three-stage life cycle: the storm builds slowly as warm air rises; it reaches maturity once the condensation gets too heavy and begins to fall; and it dies once the outflow drowns the updraft.
For the practical applications of the Thunderstorm Project, Byers was able to prove what Congress had hoped—that a trained pilot and an aircraft equipped with radar could detect and avoid the most treacherous drafts of a storm. Thanks to these intrepid test pilots, death while traveling by commercial air has become most unlikely. But for tornado science, what Byers and his cohort missed was the next leap forward. Within his own data and radar images was a notable exception to Byers’s final rule. There was one rare type of storm that didn’t quickly drown itself out; it could live and feed for hours, traveling far, growing immense. And it was this distinct breed that was the mother of the twister.
Keith Browning—an English scientist working at the Air Force Cambridge Research Laboratory in Bedford, Massachusetts—was the man who finally discovered and named the supercell. Picking up where Byers and his crew had left off, he succeeded in identifying the essential ingredients of this rare class of storm, allowing us to begin to differentiate the average rainmaker from its destructive doppelgänger.
Browning’s breakthrough came while he was studying radar imagery from a nasty 1961 tornado near Geary, Oklahoma. He noticed several peculiar attributes of the parent storm. For starters, while a line of storm cells was drifting regularly northeast, the one tornadic cell had cleaved away and was moving obstinately due east. As the other storms unleashed short-lived deluges and promptly dissipated, the lone cell continued to thrive for hours. It was also far larger than the others, standing eye to eye with the cruising altitude of a modern jetliner. More perplexingly, it exhibited a curious structure—a “vault” appeared on radar, a precipitation-free zone soaring high into the heart of the storm. What could possibly explain a persistently dry region within a proven rainmaker?
Browning found more and more storms with the same features, and he soon developed a theory: The longevity of these storms owed to an updraft on steroids. It was carving out a space in the center of the storm with velocities so intense that rain and hail simply could not fall there. This wasn’t the garden-variety buoyant column of air that would soon drown in the smothering downdraft. Browning’s updraft existed in a state of continuous reconstitution, propagating forward along a stream of buoyant, energy-suffused air like a wave on the surface of the ocean. So long as the energy source remained unobstructed, this “supercell” could conceivably continue to thrive like a perpetual-motion machine. What made the updraft in Browning’s model work was its unique ability to rotate, a quality that Byers had already noticed in some of the strongest storms. The updraft owed its freakish strength and longevity to a confluence of spiraling winds that continuously funneled warm air all the way up to the storm’s highest levels, like a fuel injector.
The supercell thunderstorm was a complex organism that required an unlikely combination of interdependent elements brought into just the right alignment. As Browning and others soon realized, nowhere else on earth do these elements seem to come together as in the North American plains. It isn’t just the hot, volatile air or the pressure cooker of the “cap” that turn the Great Plains into Tornado Alley. In the turbulent springtime months, the converging wind currents are coming from different directions, at different elevations, and at different speeds—which makes them prone to generating wind shear and the crucial rotation needed for tornadic storms. With the right winds, Browning saw, supercells pop up all along the dry line. When winds out of the southeast, the southwest, and the west—all at different levels—hit a rising column of warm air, they spin it like a top. The rotating updraft that results, what would become known as a mesocyclone, is a staple of Tornado Alley and the engine of a supercell.
As a final piece, when the mesocyclone is met by the jet stream, some six miles above the earth, the storm is able to reach its full strength. The powerful upper-level winds, in concert with the tremendous velocities of the mesocyclone, shunt the precipitation away from the throat of the storm, thereby preventing the suffocation that inevitably shortens the lives of common thunderheads. The mesocyclone and jet stream are what allow Browning’s storm vault to form.
When wind shear, the cap, a powerful jet stream, and volatile quantities of atmospheric instability pile up over the Great Plains, batten down the hatches—the titan of the sky is coming. Unlike its disorganized counterpart, the isolated supercell thunderstorm can swell to immense proportions, measuring miles across. It may contain straight-line winds capable of toppling telephone poles. Its updraft, a screaming hundred-mile-per-hour vertical vent into the atmosphere, can loft and suspend rain particles. These can then freeze and weld together into grapefruit-size hailstones, plummeting to the earth at terminal velocities. And when the rotating updraft reaches all the way down to the surface, the supercell storm has the power to summon forth the most destructive phenomenon of all, the Black Wind.
Browning was able to narrow the field of view, surmising that the vast majority of tornadoes, especially violent ones, emerged from supercells. But in his time, the tools didn’t yet exist to limn the
