Picture from NOAA
Copyright © 2007 by Ralph Couey
Written content only
Information for this article was taken primarily from “The Tornado” by Research Meteorologist Thomas P. Grazulis, who is the director of The Tornado Project, a private research and archive organization. Additional data was taken from the websites for the National Oceanographic and Atmospheric Administration (NOAA), The National Severe Storms Laboratory, and the National Weather Service.
Tornados are nature’s most violent windstorms. Born of powerful thunderstorms called supercells, their powerful winds and unpredictable nature pose a very real threat to life and property. According to the National Weather Service, the U.S. gets more tornados than any other country, around 1,200 per year. And while most seem to occur in Florida and the swath of Midwestern states known as ‘Tornado Alley,” all 50 states have experienced these storms. Anywhere supercell thunderstorms can form, the threat for tornados exists.
Hurricanes, in comparison, are enormous storms, covering thousands of square miles. But even the winds of the most powerful hurricanes ever recorded, Camille in 1969 and Allen in 1980, both 190 mph, were equal only to a medium-sized tornado.
The question of how and why tornadoes occur is still being investigated. Scientists know there are conditions within supercell storms common to tornado formation, but as to exactly what the actual trigger mechanism is, no one yet knows. Some supercells might spawn several tornados, while others with measurably identical parameters won't even form a single wall cloud.
Identifying and understanding that trigger mechanism also holds the key to determining how long a particular tornado might stay on the ground. Some have only touched down for a few minutes, while others might roar across the landscape for an hour or more. The infamous Tri-State Tornado of 1925 was reportedly on the ground for an incredible 219 miles across parts of Missouri, Illinois, and Indiana, leaving in its wake F-5 level damage and 619 dead. In recent years, meteorologists have begun to doubt that this was actually one tornado. In 1998, storm spotters recorded on video one instance where, as one tornado dissipated, another formed and strengthened within the same wall cloud. Although there were two separate twisters, the resulting damage path was uninterrupted. Some researchers suspect that this mechanism was at work in that Tri-State storm.
No one, not even an expert can rate a tornado by looking at it. There's simply too much variability in the twister's appearance to make such an assessment reliable or accurate. Tornados are rated according to the Enhanced Fujita Scale, which gauges storms based on a comprehensive damage assessment done after the tornado has passed. Such damage to a well-constructed frame home can range from shingles and windows for an EF-0 to complete obliteration in an EF-5.
While the highest rating on the Fujita scale is EF-5, some researchers think that an EF-6-level tornado could exist, with winds between 319 and 379 mph. The monstrous tornado that struck Moore, Oklahoma in May 1999 may have generated winds as high as 330 mph, according to mobile Doppler radar scans. However, since EF-5 twisters generally erase everything in their path, identifying EF-6 winds through the currently accepted method of post-storm damage assessments may be impossible to do. Still, there's something innately terrifying and apocalyptic about a storm which would have the capability to generate windspeeds equal to half the speed of sound.
Everyone should learn the basics about tornados, where to go, what to do, and more importantly, where not to go or do. Be aware, but not panic-stricken. Tornadoes are extremely rare events. They occur in only 1% of the 100,000 thunderstorms experienced in the U.S. each year. Even in the most tornado-prone areas, any given frame house probably will not be destroyed totally, on average, more than once in 100,000 years. In much of the country, that number is less often than once in 1,000,000 years. But the prudent thing is still to be alert and stay informed.
Popular Tornado Myths
Tornados have spawned a remarkable volume of myths and old wives’ tales which could prove to be deadly if believed. Here are some of the more common myths:
MYTH: The southwest corner of a basement is the safest location during a tornado.
FACT: Except in very rare circumstances, tornadoes will track from southwest to northeast. The old caution about the southwest corner came from flawed assumptions about the behavior of debris in and around a twister. In most tornadoes more houses will be shifted off their foundations rather than blown completely away, collapsing concrete foundations into that corner. Also, the leading edge of a tornado is a wind-driven blender of trees, remains of houses, vehicles, and other debris. This debris, striking the building at speeds up to 200 mph will do significant damage before the twister itself even arrives. Researcher Joseph Eagleman, of the University of Kansas, in studying the aftermath of the 1970 Lubbock, Texas tornado, found that the southwest corner was unsafe in 75% of damaged homes.
MYTH: Opening windows to equalize air pressure will save a home from destruction.
FACT: Moving one thin pane of glass will not protect a roof or a house from one of the most violent natural forces on the planet. Any structure will have many holes punched in the walls from debris circling the tornado before the center of the vortex arrives. Such debris strikes will blow more than enough ventilation holes in the building. Besides, even the center of a mature EF-4 will have a pressure drop of only about 1.4 pounds per square inch, while the winds circling outside the center of that EF-4 pack pressures of more than 100 pounds per square inch, enough force to destroy most structures.
MYTH: Highway overpasses can provide emergency shelter from an approaching tornado.
FACT: This is one of the most dangerous misconceptions. Some of the people who followed this example during the May 1999 Moore, Oklahoma tornado paid for this misinformation with their lives. Narrow spaces like those under an overpass, will actually funnel and compress winds, making them more powerful, literally sucking some victims out from under the bridges, and bombarding the others with debris. In open country, a shallow ditch away from buildings or trees will give you better odds for survival. During the Moore storm, one man stopped his car and sent his wife and two of their children on ahead to an underpass, while he stayed behind to remove the youngest child from a car seat. The twister caught the man and his infant out in the open and he dove into a shallow ditch. The storm swept the underpass, killing the wife and the two children. The man and the infant in the ditch survived with cuts and bruises.
MYTH: More numerous and violent tornados are occuring now than at any time in history.
FACT: As late as the mid-60's, a tornado wouldn't be counted unless it was actually seen by a qualified observer, or identified through a post-storm damage assessment. There were probably many twisters that may have torn through open fields for a few hundred yards and disappeared. With no damaged buildings to assess, no one could count the tornado. However, with the advancements in Doppler radar technology, and especially in computer processing capabilities, many more twisters are now identified via radar that would have been completely missed before. Also, the denser population and the explosion in qualified storm spotters results in many more "eyes" on a given storm than ever before. There are even private companies out there who, for about $2,000 a week, will take you on a tour where you and your fellow travelers will actually chase tornados. (And here I always thought vacations were for relaxation...) The combination of these elements has led to an increase in verified sighting reports, but as to whether the number is currently higher than in previous decades is statistically impossible to answer due to the vast improvement in the frequency and quality in data collection between then and now.
Awareness is the key to tornado safety, staying alert to local weather conditions and knowing the proper safety procedures for any of the variety of places and situations you might find yourself in. You should never count on more than 3 minutes warning, or at night, 30 seconds to 1 minute. Therefore, you should have an emergency plan in place and practice it with your family at home and co-workers on the job.
On severe weather days, a local media outlet – commercial radio, NOAA weather radio, or television – should be monitored closely. If you have cable or satellite television, tune to a local channel. A tornado warning for Cambria County, Pennsylvania won’t be carried by WTBS in Atlanta.
Sirens are a vital part of the local warning process, but you should not depend on them. They may not be sounded in time or even sounded at all. This could be due to a power outage caused by the storm or failure of the siren itself. The violent cacophony of severe thunderstorms may even cover up the sound of the siren. Also, in smaller communities, the same siren that calls out the local Volunteer Fire Department also sounds the storm warning, causing a momentary and perhaps fatal hesitation. Be sure you understand what the siren means in your community. Different communities have different philosophies about the use of a siren. City or county officials can give you that information.
Going out and looking for a tornado is not a smart thing to do. The mountainous terrain of southwestern Pennsylvania almost always blocks a clear view of the horizon. An approaching tornado will be screened by the intervening hills and possibly shielded by the parent storm’s intense curtain of rain. These parent storms also develop hail shafts, dropping golf- or baseball-sized chunks of ice, shattering winshields. No one should have to explain the consequences of head trauma caused by such objects. The restricted visibility means that you could walk or drive right into a tornado and not realize it. Remember also that the twister is continually ‘inhaling’ debris, ranging from rocks and trees to vehicles and parts of buildings. Whatever goes up, must come down, which makes anyplace within about a mile of the tornado a deadly dangerous place to be.
Your first response should be to get to shelter, not be to grab the camcorder or run to a window. To be exposed to high winds and debris risks serious, even fatal injury.
In a house without a basement, go to the lowest level of the structure, avoid windows, and put as many walls as possible between you and the tornado. Go to an interior closet or bathroom with no windows. The short-span walls may provide a life-saving additional degree of strength. Cover your body with a sleeping bag, cushions, or blankets. Protect your head as much as possible, perhaps using a metal trash can lid. Stay away from the southwest corner of the house.
It is not uncommon to see only the bathtub remaining on the lower floor of a house in the aftermath of a tornado. The tub can be a planned destination if you have only a few seconds warning. A bathroom often has extra bracing used to hold the fixtures, as well as additional reinforcement provided by the pipes in the walls. Also, in a house without a basement, the tub and commode will be anchored to the foundation.
The safest place is in the basement, but you still need something sturdy under which you can hide, like a workbench or a staircase. Also, make sure that place is not below a heavy object such as a piano on the first floor and not in a path likely to be taken by a falling chimney. Be sure that the entire family is aware of the location of the safest area ahead of time, especially children of working parents who might be home alone during the period of time between 4 pm and 8 pm when most tornadoes occur.
Office Buildings and residential high-rises
Office buildings offer unique challenges. The guideline about basements certainly applies. Barring the time to reach that shelter, the next best thing is to go to an interior hallway or restroom, as far away from windows as possible. Crouch down on the floor next to the wall and protect your head. If you have little or no warning, get under your desk and protect your head. Structures made of steel-reinforced concrete can usually survive most tornados, but their weak points will be windows and doors. Even though the building itself may survive, broken windows and doors will admit the very high winds and debris as the twister passes.
Schools, churches, and other large buildings
Appropriate authorities should have detailed and specific lists of safety rules in advance. Buildings are built so differently that each one needs its own unique set of emergency plans with designated shelter areas. However, some general rules do apply.
The best shelter is provided in interior hallways in areas with short-span roofs and walls and containing as few windows as possible. Avoid auditoriums, gymnasiums, cafeterias, libraries or any other rooms with large unreinforced walls and/or tall and/or wide-span roofs.
Long-span buildings such as factories, warehouses, and large retail stores can be especially dangerous, since most or all the entire roof structure is supported by the outside walls. As the tornado approaches, the force of high winds and debris strikes can cause the failure of the windward walls, and subsequently the ceiling with catastrophic results for the occupants. Restrooms are among the safest areas. Their plumbing, short span walls, and metal partitions add strength. In a pinch, the corner of a building away from the tornado’s approach might be safer than the middle of a long wall.
Keep in mind also, that in a factory or other industrial building that tools, carts, raw materials, anything lying around loose, will become missiles if a tornado strikes the building. There have been many documented examples of seemingly flimsy things like corn stalks being driven like spikes into walls and telephone poles. Imagine the danger of a hammer or a set of screwdrivers blown around by 150-mile-per-hour winds.
If you’re at the mall, you will probably not even know about the twister until it actually strikes the building. Immediately go to the nearest small store and get under a non-glass sales counter. This is merely the best of a lot of bad options in that situation.
If there is no time to go anywhere, get up against heavy shelving, under heavy counters or workbenches, anything that will support or deflect flying or falling debris.
If You’re Caught Outside
If you’re caught outside in an open area, run at right angles to the tornado’s path and locate a ditch, gully, or other depression. Lie flat and protect your head. The ditch you seek should be away from the tornado and not close to large trees. Stay away from forests or even small groves of trees. Even straight-line thunderstorm winds can cause a multi-ton tree to fall on you.
Sunken pipes and drainage systems can be tempting, but remember that pipes can funnel and compress winds just like underpasses. Remember also that tornadoes are always a part of supercell thunderstorms, which can drop torrential amounts of rain in a very short period of time. Drainage pipes will fill quickly and that poses a very real drowning risk, especially if the ends become blocked by debris.
A motor vehicle is an extremely dangerous place to be in a tornado. In the Pampa, Texas tornado of 1995, full size pickup trucks were seen on video flying around the outside of the tornado as much as a hundred feet in the air before being thrown to the ground and smashed to a thickness of about three feet. In the famous Andover underpass video, if you look carefully at the approaching tornado, you can see a black minivan being tossed around the vortex like a piece of cardboard. That example is critical because that particular twister was relatively weak, at most a strong EF-1. The standard safety guidelines for cars are to stop the vehicle and get away so it does not roll over on you.
In a city, falling buildings, flying debris, and downed power lines can rapidly block streets. In places like Johnstown or Somerset a lot of the buildings are made of unreinforced masonry or brick, which have potential entrapment hazards if the structure collapses. Bricks can also become missile hazards in the high winds. Tall buildings will be the source of falling shards of glass. Trying to outrun a tornado in a car under these conditions is suicide. Buildings block the line of site, and the grid-like layout of city streets can keep you from getting to an escape route. Other drivers foolish enough to be in their vehicles will be watching the sky, not the streets, so a collision is highly probable.
Outside of town, visibility will be better, but tornadoes do not always move in predictable paths. The forward motion of some tornadoes has been clocked as high as 70 mph and while cars are restricted to roads, tornadoes are not. Many have been seen to whip back and forth along their forward path, several hundred yards in each direction.
The last place, literally, anyone should be in the face of a tornado is inside a mobile home. Mobile homes are not made of reinforced materials, nor are they firmly attached to foundations and will literally be shredded by the twisters winds. If your community or park does not have a common underground shelter, you should pick a place outside the home that you can get to in a hurry. The previous advice about ditches and low-lying places away from trees and tumbling vehicles certainly applies here.
Forewarned is Forearmed
During any severe weather event, keep a watch on the skies and never be far from a battery-powered radio. Remember that tornados can form quickly and unpredictably. Never feel foolish about seeking shelter if you suspect the situation calls for it. Make sure your family, especially children, know what to do and where to go before the storm hits, and where to meet after the storm passes. Formulate an emergency plan and practice it! Above all, try to keep yourself from being lost in an absolute panic. Knowledge, practice, and awareness can help you keep your head. And save your life.