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Tornadoes: Terror Along Tornado Alley
By Joan Whetzel
Every spring marks the beginning of tornado season in Tornado Alley, an area of the continental US covering part or all of 18 States. When spring is near, these states must prepare for tornado season. Weather forecasters can predict the weather that stirs up tornadoes more easily these days due to the hard work of tornado chasers and a wealth of information recorded since the turn of the 20th century about tornadoes and the mess they .leave in their wake. Teachers and parents can help their students become tornado experts through investigation of these treacherous vortexes and the storms that spawn them.
Tornado Alley covers 18 states in the central Unite States. The area includes most of North Dakota and Texas, all of South Dakota, Nebraska, Kansas, Oklahoma, Louisiana, Arkansas and Missouri, most of Indiana and Illinois, western Ohio, western Kentucky, western Tennessee, and far eastern Colorado and Wyoming. On average, the US has over 100,000 thunderstorms every year, producing over 1,000 tornadoes of varying degrees. Most of the tornadoes in the US each year are F0 and F1, with only about 1% of all tornadoes in the US reaching F5 status.
Tornadoes can hit any time of year, following the development of severe thunderstorms. They tend to hit in higher concentrations in the spring, though they generally occur anywhere from March to October, with over 80% of them occurring in the afternoon and evening. Tornadoes arise from thunderstorms turning into spinning vortexes with wind speeds that can reach up to 192 miles an hour. When they drop from the clouds to the Earth's surface, that's when they cause all the damage. They spin in a counterclockwise direction, travel in a northeasterly direction, covering about 18 miles at a stint, and can last up to 30 minutes. While predicting the thunderstorms that generate them is easy, predicting the tornadoes is still an developing science.
The Fujita Scale, which was developed in 1971, help scientists and meteorologists identify the tornadoes by category as they appear. By regularly studying the thunderstorms and tornadoes, they are beginning to get a handle on predicting tornadoes, or at least, in predicting the storms most likely to produce them.
Tornadoes usually develop from squall lines and super-cell thunderstorms, when a layer cool air rides up over a layer of warm air, forcing the cool air quickly upward. Meteorologists look for a distinctive "hook echo" on their radar which indicates possible tornado formation. Tornadoes are invisible after dark, though they sometimes develop a glow. Some daylight tornadoes can be almost invisible, with the only thing marking their existence being the debris they kick up. They may appear quickly and with little or no warning, making it impossible to run and difficult, at best, to get to safety. Most of the tornado induced damage to man-made structures is a product both the high wind and the debris kicked up by these storms.
Not all thunderstorms, super-cells, or squall lines churn out tornadoes. The right combination of atmospheric conditions (e.g. wind, temp, barometric pressure, humidity) are necessary to stir up even the weakest of tornadoes. All tornadoes, from the weakest to the strongest share, these same characteristics:
1. They are micro-scale rotating areas of wind. While some thunderstorms rotate, they don't have all the features that would characterize them as tornadoes.
2. Their rotating winds (vortex) must be connected to a convective cloud base and be touching the ground at the same time.
3. They must have caused enough damage to be classified as tornado using the descriptors listed on the Fujita-Pearson scale.
Tornado Watches and Warnings
When thunderstorms occur, tornado watches and warnings may be issued, provided the conditions warrant it. Tornado watches mean that the conditions are ripe for tornado formation. Warnings are issued when severe thunderstorms with tornadoes are about to strike. With tornado warnings, the public is directed to find safe shelter in rooms or hallways without windows, on the ground floor if possible, or in doorways and under strong furniture. However, people are strongly urged to leave mobile homes and take shelter in stronger buildings.
When traveling in cars, drive out of the tornado's path if at all possible. If not, park the car out of the main lanes of traffic, and seek shelter inside a sturdy building or in a mud ditch. It is not recommended that motorists park under bridges, since not all bridges are constructed well enough to withstand damage from tornadoes. People have been injured or killed as tornadoes passed over bridges that they were hiding under.
Fujita Pearson Scale
Japanese engineering professor, Theodore Fujita, spent a lifetime studying tornado damage, which led to the development of the Fujita Scale in 1971. The chart lists tornadoes by scale (F0 to F6), category (weak to violent), force (wind strength), path length (in miles), path width (in miles or yards) and damages caused. In 1973, Dr. Fujita wrote a paper on tornadoes with Dr. Allen Pearson, who headed the National Severe storms Forecast center. They upgrade the tornado scale to the Fujita-Pearson scale which added more information to the descriptions of the tornado width and path
While no one can be totally prepared for a tornado, there are things everyone can do to be ready in case that one will occur in their area. Anything you can do to improve your chances of surviving a tornado is worth the trouble.
- Be alert to changed in the weather and look for approaching storms.
- Be aware of the common tornado danger signs: dark, greenish-colored skies; large hail; huge, dark, low clouds (especially if they're rotating); and loud wind sounding like a freight train.
- Purchase a NOAA weather radio and check the batteries regularly. Keep an extra supply of batteries in the event that power outages may be long lasting.
- Keep an emergency supply of blankets, nonperishable food, can openers, clothes, flashlights and batteries, where you can safely easily get to them. Keep them in your home's safe area or storm shelter, if possible.
- Purchase or create a first aid kit.
- Know where storm shelters are located in your community.
- Make sure you have several days worth of all necessary medications on hand.
Here a few projects that teachers and parents can do to help their children learn about tornadoes.
1. Tracking Storm Cells. Use city maps to pinpoint locations where tornadoes have struck or have been sited. In a spiral notebook, record the date and time when thunderstorms hit your area. Record all tornado watches and warnings. Record any tornado sightings as well as actual tornadoes touching down, along with the scale, category, force, path width, path length, and damage left behind. Let them see if they can use this information to make predictions of their own.
2. Fujita-Pearson Scale Investigations.Have students locate copies of the Fujita-Pearson Scale and the Saffir-Simpson scale on the internet. Have them compare both charts for similarities and differences in what they both measure and how they assess damage. Open the class to discussions about which storm type causes more damage, which creates stronger winds, and how this information can be used to make building codes better and to reduce or eliminate storm damage.
3. Tornado Alley Investigation. Have students locate a map of the Tornado Alley States. Have them look up tornado data for those 18 states and compare that to the tornado data for the rest of the 50 states. Create a Tornado Alley data table for each of 3 years (this year and the two previous years) with columns for the state, tornado scale and category and record tornado counts for tornadoes in each scale for a given year. Compare the results. Determine which states had the most and least tornadoes in each scale. Discuss what this information means.
4. Tornado in a Jar. Help students visualize what a tornado looks like with this experiment. Fill a clear jar 3/4 full with water and add 2 TBSP of dishwashing liquid and a marble. Place the lid on the bottle, being careful to twist it tightly closed. Have the students swirl the jar, watching closely as the vortex forms.
5. Signs of a Tornado. Split the class into four groups. Have the first group perform computer searches to gather information on tornado watches and warnings. The second group will perform computer investigation on signs of an impending tornado. The third group will look up information on tornado preparedness and tornado safety. The fourth group needs to locate information on ways to help the community clean up after a tornado. Once they groups have compiled their information, each will make a presentation to the rest of the class. Afterward, open the class up to discussions on weather conditions that create tornadoes, predicting tornadoes, what they can do to create at Tornado Disaster Preparation Plan classroom for their classroom, and how their class can help the community clean up after a hurricane strikes.
Studying tornadoes the causes and effects of these frightening events. Some people may even find that understanding what's going on and what they can do before, during and after a tornado, helps them to ride out the storm. Better yet, students can even post the results of their investigations and their ideas for solutions on the school's webpage, which adds to the wealth of information available to meteorologists.
Tornado Chaser: Make a Pet Tornado. Downloaded 1/2012.
Tornado Chaser: Where Is Tornado Alley?. Downloaded 1/2012.
All Science Fair Projects: Tornado. Downloaded 1/2012.
Discovery Education: Library Lesson Plan --- Tornado!. Downloaded 1/2012.
Tornado Project: Fujita Scale. Downloaded 1/2012.
NOAA: US Tornado Climatology. Downloaded 1/2012.
NOAA: The Online Tornado FAQ. Downloaded 1/2012.