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Assessing Your Tornado Risk in Tornado Alley

 Tornado Occurrence in “Tornado Alley”

“Tornado Alley” is an area of the U.S. heart-land known for its tornado activity. Although the boundaries of Tornado Alley can be debated, most scientists agree that Texas, Oklahoma, Kansas, and Nebraska are well known for tornado risk and make up a large portion of Tornado Alley. Tornado risk includes the potential for property damage, injury, and loss of life all of which are increased with a higher frequency of occurrence.

Tornado Alley’s climate and location are ideally suited to create supercell thunderstorms, which commonly spawn violent tornadoes. As in the rest of the United States, the majority of tornadoes in Tornado Alley are typically weak or moderately strong (classified as EF2 and smaller on the Enhanced Fujita Scale). However, even these weaker tornadoes can be deadly. Further, tornadoes are not always single tornado events; sometimes outbreaks of several tornadoes are associated with a large storm system. This type of tornado outbreak happens frequently in Tornado Alley due to the supercell thunderstorms that affect the area. In fact, there have been two such occurrences in the recent past in the Midwest.

 

The Great Plains Tornado Outbreak of May 3, 1999 Over 70 tornadoes occurred during this outbreak in Oklahoma, Kansas, and Texas, 4 of which were considered violent (F4 or F5) An F5 tornado struck the Oklahoma City area, two F4 tornadoes struck populated areas north of Oklahoma City, and one struck the Wichita, Kansas area 49 people were killed and approximately 800 were injured Over 2,000 homes were destroyed and more than 7,000 were damaged Damage was estimated at $1.2 billion.

In the May 8, 2003 Outbreak An estimated 80 tornadoes touched down throughout 8 states Significant damage was reported in Kansas, Oklahoma, and Missouri, including the Kansas City and Oklahoma City areas 37 deaths were reported In Oklahoma, an estimated 300 homes were destroyed and 1,500 were damaged.

Assessing Your Risk to Protect Yourself

Step 1: To determine your exposure to a low, moderate, or high tornado risk, use the Frequency Map below to determine how many tornadoes were recorded for the area where you live located. Then Find the row in the “Risk Table” below that matches that number.

Tornado risk map

 

Tornado Risk, learn to protect yourself, chart

 

Step 2: look at the Wind Zone Map below and note your wind zone (I, II, III, or IV). Find the matching column in the Risk Table and look for the box where your frequency row and wind zone column meet. Your risk level is given in that box and helps you assess the need for a shelter.

wind zones used to protect yourself by calculating your risk of Tornado strength. Map.

 

 A shelter is the preferred method of protection in high-risk areas. Example: If your building is located in Wichita, Kansas, note that Wichita is in an area shaded red on the Frequency Map. According to the map, the number of tornadoes in the Wichita area is >25. On the Wind Zone Map Wichita is within Wind Zone IV. The box in the Risk Table below where the >15 row and the Zone IV column meet is shaded dark blue, which shows that the building is in an area of high risk.

 Can a Building Survive a Tornado? Building to Protect Yourself

Yes! High-wind shelters can be designed and constructed to protect occupants from winds and windborne debris associated with all tornadoes (EF0–EF5). Buildings designed and constructed above basic code requirements (also known as “hardened” buildings), and newer structures designed and constructed to modern, hazardresistant codes can resist the wind load forces from weak tornadoes (EF1 or weaker). Even strong tornadoes have wind speeds away from the center or vortex of the storm that can be similar to building code level wind speeds. Much of the damage is caused by winds rushing toward and being pulled into the tornado itself. Many newer homes designed and constructed to modern codes, such as the International Residential Codes (IRC 2000 Edition and newer), may survive without structural failure if struck by weak tornadoes or if located on the periphery of the paths of strong tornadoes. The primary damage to these newer homes is to the cladding and exterior systems: roof covering, roof deck, exterior walls and windows. For most building uses, it is economically impractical to design the entire building to resist tornadoes. However, portions of buildings can be designed as shelters to protect occupants from tornadoes. For information on designing shelters to resist tornadoes, see the Tornado

Storm Shelters: Selecting Design Criteria

Residential Sheltering: In-Residence and Stand-Alone Shelters.

Weather Radios Essential For Survival and Protection

All individuals living or working in tornado-prone areas should have a weather radio inside their home or place of work. A weather radio is particularly important for those living in an area that does not have storm warning sirens. The National Oceanic and Atmospheric Administration (NOAA) Weather Radio (NWR) is a nationwide network of radio stations broadcasting continuous weather information directly from a nearby National Weather Service (NWS) office. NWR broadcasts NWS warnings, watches, forecasts, and other hazard information 24 hours a day, and post-event information for all types of hazards, both natural and technological. NOAA Weather Radios are available at electronics stores across the country and range in cost from $25 to $100 or more, depending on the quality of the receiver and number of features. The NWS does not endorse any particular make or model of receiver.

Features to look for in a NOAA Weather Radio

 The most desirable feature is an alarm tone. This allows you to have the radio turned on but silent, listening for a special tone that is broadcast before watch and warning messages that give immediate information about a life-threatening situation. Specific Area Message Encoding (SAME) technology, a feature available since the mid-1990s, is capable of providing detailed, area-specific information. Unlike other NOAA Weather Radios, the SAME feature will filter out alerts that do not affect your immediate area. It should operate on batteries during times when electrical service may be interrupted. Look for radios with an AC adapter and battery compartment. The radio should be tunable to all seven NWR frequencies. For the latest list of frequencies and transmitter locations, check the NOAA Weather Radio Web site http://www.weather.gov/nwr. The hearing and visually impaired can receive watches and warnings by connecting weather radio alarms to other kinds of attention-getting devices, such as strobe lights, pagers, bed-shakers, personal computers, and text printers.

Other methods to receive forecasts, watches, and warnings directly from the National Weather Service

Tune in to your local radio and television stations for the latest weather forecasts, watches, and warnings. NWS products and services are also available on the Internet at http://www.weather.gov/nwr. Delivery of data across the Internet, however, cannot be guaranteed because of potential interruption of service. Another low-cost method for receiving essential information is to use a wireless data system called the Emergency Managers Weather Information Network (EMWIN). This system presents the information directly on your home or office computer. Users can set various alarms to go off to be alerted to particular information, whether for their local area or adjacent areas. For more information, visit the EMWIN Web site http://www.weather.gov/emwin/index.htm.

 

 

 

 

Useful Links and Resources

 Taking Shelter from the Storm: Building a Safe Room Inside Your House (FEMA 320), March 2004,

2nd Edition Design and Construction Guidance for Community Shelters (FEMA 361),

July 2000 Tornado Protection: Selecting Safe Areas in Buildings (FEMA 431), November 2003  

 

This Information is courtesy of the hard working individuals at FEMA, Tornado Risks and Hazards in the Midwest United States

 

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