Twisting in the Wind: Tornado 101

James Carafano /

As Hurricane Irene heads toward the East Coast of the United States, we also have to worry about tornadoes. Tornadoes often form as a result of hurricanes.

Tornado conditions can be predicted, but actual storms cannot. The National Weather Service issues tornado watches (a tornado is possible) and warnings (a tornado has been sighted). They are massive rotating funnel-shaped columns of air that extend from a thunderstorm formation. The columns are transparent, but as they accumulate dust and debris, they take on the shape of a dark spiraling cloud.

The destructive force of the tornado comes from the shearing force of the rotating wind, which can reach over 300 miles per hour. Funnel clouds on the ground can reach one mile wide and make contact for up to 50 miles. Tornadoes have been recorded with forward motion up to 70 miles per hour; an average tornado speed is about 30 miles per hour. Storm fronts and hurricanes may spawn multiple tornadoes.

The general size of a tornado does not indicate its severity. That is measured on the Fujita scale, developed by examining the damage caused by tornadoes. It represents a subjective judgment of damage. The scale starts with F0, a storm with rotating wind speeds of 40 to 72 miles per hour. Typical results of an F0 are described as “some damage to chimneys; breaks branches off trees; pushes over shallow-rooted trees; damages sign boards.” The highest ranking is an F6, with wind speeds of 319 to 379 miles per hour. Storms this intense cause “strong frame houses lifted off foundations and carried considerable distances to disintegrate; automobile sized missiles fly through the air in excess of 100 meters; trees debarked; steel reinforced concrete structures badly damaged.”

Although tornadoes can occur in any state, according to the Federal Emergency Management Agency (FEMA), tornadoes appear most frequently east of the Rocky Mountains during spring and summer months. Tornado “season” in southern states lasts from March to May and in northern states from late May to early July.

Destructive winds are the most significant threat. In addition, flying debris can cause significant damage. Tornadoes in the United States cause an average of 70 fatalities and 1,500 injuries each year. In addition, these storms can significantly damage buildings and infrastructure. Hail damage is also common, as are local power outages. Danger is greatest when tornadoes are part of a complex weather event, such as hurricanes, major thunderstorms, or floods.

Early warning is the single most important factor for limiting loss of life. Even a few minutes’ warning may provide time for individuals to seek shelter, which is the most vital disaster response measure. In the wake of the storm, housing for displaced people may be required.

Because of the potential for injuries and destruction, many kinds of first responders may be required. National Guard units may be deployed. States may also use emergency management assistance compacts to obtain support from adjacent states. Depending on the level of destruction, states may request federal assistance. Federal response assets would be coordinated through FEMA regional headquarters. In particular, FEMA-managed urban search-and-rescue teams may be deployed.

While the effects of tornadoes are often localized, they can impact a large geographical area covering a number of jurisdictions. In many parts of the United States, they are a familiar, annual menace. On May 21, 2011, a single tornado plowed through a 13-mile strip in Joplin, Missouri, killing more than 150 people. Estimates of the damage from the storm range up to $3 billion. Only a month earlier, tornadoes had swept through the same state, leaving enough damage to prompt a presidential disaster declaration.

FEMA provides general guidance for what to do before, during, and after a hurricane. States also provide information on their emergency management websites. FEMA also provides an index with contact information on state agencies.

The sad truth is we may be as prepared as we could be for the kinds of threats the nation may face this weekend. Heritage homeland security expert Matt Mayer points out that FEMA “has been responding to almost any natural disaster around the country, be it a contained three-county flood, or a catastrophe of near-epic proportions like Hurricane Katrina. As a result, many states and localities have trimmed their own emergency-response budgets, often leaving them ill prepared to handle even rain or snowstorms without federal assistance. This leaves FEMA stretched far too thin and ill prepared to respond to grand-scale catastrophes.”