Tornadoes: Formation, Destruction, and the Spencer Tornado

Introduction to Tornadoes

Tornadoes are among the most violent and unpredictable natural phenomena on Earth. This paper examines the basic science behind tornadoes and explores a specific historical example — the May 30, 1998 tornado that struck the tiny town of Spencer, North Dakota. Tornadoes differ from hurricanes in that they form over land, while hurricanes form over water. They differ from cyclones in that they travel over a much smaller area. Although tornadoes tend to be localized, they can cause massive structural damage and significant loss of human life. They are difficult to predict, and so far no scientist or research group has been able to develop a reliable tornado early warning system capable of consistently saving lives and preventing property damage.

How Tornadoes Form and Are Classified

Scientifically, tornadoes develop when certain atmospheric conditions align. They form as a result of a heavy cumulonimbus cloud mass present in the atmosphere, particularly during the hot, humid weather of Midwestern U.S. summers. The atmospheric conditions required for tornado formation include vast thermal instability, high humidity, and the collision of warm, moist air at low altitudes with cooler, drier air above. When these conditions come together, a funnel cloud with very low air pressure descends from the cloud mass and reaches the ground. Inside this funnel, winds rotate counter-clockwise with violent force.

These conditions are most common during the late spring and early summer months across much of the continental United States, making tornadoes a recurring threat to large metropolitan areas in the Midwest. The word "tornado" itself comes from Spanish, meaning loosely "turn." People often call tornadoes "twisters" or "cyclones," though tornadoes are not technically cyclones. Their distinctive funnel cloud is typically wider at the top and narrower at the bottom. Wind speeds inside a tornado can reach extraordinary levels — they have been recorded at as high as 318 miles per hour, though most average between 100 and 150 mph.

An average tornado is roughly 300 to 400 yards wide, though some have been measured at a mile or more across. They "travel haphazardly along paths from several miles to fifty miles, most often in a southwest to northeast direction and are associated with very low barometric pressure readings and heavy rains" (Resnick 125). Tornadoes are often spawned during thunderstorms and can also be associated with heavy hail or sleet. As Resnick notes, "Twisters tend to strike in pairs within a short period of time in nearby locations" (Resnick 126).

The worst tornado on record in the United States occurred on March 18, 1925. It cut across a wide swath of three states — Missouri, Illinois, and Indiana — remained on the ground for over three hours, and left nearly 700 people dead (Resnick 126). Tornadoes are rated on the Fujita scale, named after Tetsuya Fujita, a Japanese scientist who specialized in tornado and wind research. An F-5 is the strongest and deadliest classification. An F-3 produces winds up to 206 miles per hour; an F-4 features winds between 207 and 260 miles per hour; and the most dangerous category, F-5, involves winds from 261 to 318 miles per hour (Rosenfeld 192).

Tornado Prevalence and Historical Impact

Tornadoes have occurred on every continent except Antarctica, but they are most prevalent in the United States — particularly in the region known as "tornado alley," which stretches across the mid-section of the country from the southern plains states to the Gulf states, with Texas, Kansas, and Oklahoma being especially vulnerable. However, tornadoes can and do strike many other parts of the country when conditions are right; they are simply more frequent in tornado alley than anywhere else on Earth. Jeffrey Rosenfeld notes that approximately one thousand tornadoes hit the United States in any given year (Rosenfeld 4). While many of these tornadoes cause limited structural damage, a significant number do not, and it is those storms that attract national media attention. As one source states, "During a seventy-year period, 1925–1995, as many as 4,944 people died from tornado disasters in the United States. From 1967–1996, deaths from tornadoes averaged 70 each year" (Resnick 125). Deaths and injuries are only part of the story; tornadoes also cause millions of dollars in property damage annually.

Conclusion

Tornadoes are one of the deadliest atmospheric phenomena known to humankind, and they strike the United States with predictable regularity every year. The atmospheric conditions in tornado alley create ideal circumstances for tornado formation during late spring and early summer. Until scientists develop more reliable methods for predicting these destructive storms before they touch down, individuals, cities, and even entire towns may remain vulnerable to the dark funnel clouds that twist suddenly and violently across the American landscape.

References

Resnick, Abraham. Due to the Weather: Ways the Elements Affect Our Lives. Westport, CT: Greenwood Press, 2000.

Robertson, David. "Beyond Twister: A Geography of Recreational Storm Chasing on the Southern Plains." The Geographical Review 89.4 (1999): 533.

Rosenfeld, Jeffrey O. Inside the World's Deadliest Hurricanes, Tornadoes, and Blizzards. New York: Plenum Press, 1999.