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Weather Information



     A tornado is an intense, rotating column of air extending from the base of a thunderstorm cloud to the ground. Tornados have occurred in all 50 U.S. states. The majority of them, though, occur in what is known as "Tornado Alley". Tornado Alley covers the area from central Nebraska southward to Central Texas. The wind speeds within a tornado vary from 72 to over 300 mph. The wind produced by a tornado are the most violent that occur on earth. An average of 2% of tornados worldwide have speeds of over 200 mph. In the U.S. and the rest of the northern hemisphere, Tornados rotate counterclockwise and rarely do they rotate in the opposite direction. Most tornados usually last less than an hour with travelled distances of about 20 miles. Tornados happen more often in the spring and early summer but can occur any time of the year.

     A tornados life has four stages; organization stage, mature stage, shrinking stage and the decaying stage. The funnel funnel usually appears and touches down in the first stage. In the second stage, the tornado is usually the largest and more mature, hence the name "Mature Stage". In the shrinking stage, the funnel thins out to a skinny column and becomes fragmented. While dissipating and disorganizing in the decaying stage, it can still be very destructive.

     The surroundings within a storm must almost be perfect for a tornado to form. Supercells, which are massive storms, are formed from warm, moist air colliding with cool, dry air. Tornados occur more often in Tornado Alley because the Gulf of Mexico supplies the warm, moist air and Canada supplies the cool, dry air during the spring and summer months. Once these two opposing air meet, the warm air rises and condenses to form the clouds. Warm air rising very quickly forms an updraft which causes the tops of a storm to grow much higher, sometimes as high as 10 miles. High winds in the upper atmosphere can blow the high tops of a storm over producing anvils. Usually, the area under the anvils is rainfree. Rain falls to the northeast of the anvil.

     A squall line is an area of cooler air in front of a cold front and also an area of instability where supercells form. The cooler air in a squall line meets the warmer air first which can form very severe storms. The extreme organization in a supercell is the reason its called "super". Most storms have several updrafts and downdrafts which interfere with each other; whereas a supercell only has one updraft and one downdraft which allows it to feed off itself giving it a long and intense life. Supercells often produce gusty winds, heavy rain, large hail and sometimes tornados.

     Wind shear is wind blowing at different directions at different altitudes and speeds which causes air around it to rotate horizontally. When this horizontal column of air meets with one of the strong updrafts, it becomes twisted and bent upward. This mass of rotating air is called a mesocylcone. This area of rotating air is where the tornado will most likely form. Wall clouds, which are lowerings of the clouds base in a specific area, are usually seen prior to a tornados development.



     Within a tornado funnel can be several smaller funnels called "suction vortices". A tornado usually has around 1-6 suction vortices at any given time. The width of these suction vortices depends on the overall width of the tornado but are normally between .5-50 meters in diameter. They can be stationary or rotate around the center of the tornado and contain the strongest winds within the tornado. A complex pattern of narrow trails of debris is often left behind a tornado with multiple suction vortices. These tornados are among the most destructive. Suction vortices have been known to contain vortices themselves.

     With winds reaching as high as 300 mph, tornados can do quite a bit of destruction. Damage to buildings and heavy objects flung about like toys reveal the extreme wind speeds associated with tornadoes. One theory for the amount of destruction to buildings is related to a great drop in atmospheric pressure as the funnel passes overhead. This theory has its points, however most scientists seem to believe that the force of the wind is responsible for the destruction. This can be proven by the way buildings collapse when hit by a tornado. The southwest walls, which usually face the strongest winds, generally fall inward, knocked down by the strength of high sustained winds. This is one reason why people are told now to not bother opening their windows, as this won't help equalize the pressure, and will only waste time getting to cover instead.

     Some scientists theorize that tornadoes which cause heavy damage more often than not are tornadoes with multiple vortices. These vortices rotate around each other within the funnel, and are responsible for most of the damage caused by a tornado. Professor Fujita, of the University of Chicago was one of the first scientists to study these multiple suction vortices. Professor Fujita also was responsible for studying the damage left in the wake of tornados. He came up with a scale which is widely used today to categorize tornados, based on their destructiveness. This scale is known as the Fujita Scale.

The Fujita Scale
Strength Description Wind Speeds
F-0
Gale 40 to 72 mph
F-1
Moderate 73 to 112 mph
F-2
Significant 113 to 157 mph
F-3
Severe 158 to 206 mph
F-4
Devastating 207 to 260 mph
F-5
Incredible 261 to 315 mph
F-6*
Inconceivable 316+ mph
This F-scale is used by surveying the degree of damage which a tornado has caused. This method works well for estimating the intensity of a tornado, however, since damage is required for an estimate, tornadoes which occur in the open country are hard to categorize.
* An F-6 tornado has never been observed. This is a theoretical value which lists the strongest storm estimated to be possible. Although, the 3rd of May in 1999, the devastating tornado that hit Moore, Oklahoma had the strongest wind speeds ever recorded and was the most destructive tornado to date. The series of 55 tornados that hit took 44 lives and caused over 1.3 billion dollars of damage. The wind peaked at 318 mph, which should have been classified as an F-6, but instead was classified as an F-5.

     On the topic of Destruction comes the story of the Tri-State Tornado. This tornado killed 695 people, injured 2,027, and caused $16.5 million dollars in damage (over $50 million dollars today), all in a time period from 1:00 to 4:30 pm. Four towns were completely obliterated, and six more towns were damaged. The tornado began in Missouri at around 1:00 pm. The town of Annapolis, Missouri was destroyed first, as the tornado whipped through the state at 72 mph. The tornado entered the state of Illinois at the town of Gorham, which was completely destroyed. Once in Illinois, the tornado grew to a chilling one mile wide on the ground. Most of the loss of life was suffered in Illinois because the funnel appeared as a large amorphous cloud rather than a deadly tornado. A pressure of 28.87 inches was recorded in West Frankfort. The next town to be wiped off the map was Griffin, as the tornado crossed over the Wabash River and into Indiana. Once in Indiana, the Tri-State picked up speed to 73 mph again. The tornado finally dissipated northeast of Princeton, Indiana. The tornado lasted a record three and a half hours and covered a distance of 219 miles.

     The Tri-State Tornado is by far the worst tornado on record. The destruction caused by this one event is amazing. Thanks to weather satellites and today's advanced warning systems, such as the NEXRAD (Next Generation Radar) system, much loss of life cab be prevented. However, scientists are still unsure of how the Tri-State Tornado would affect us today. The storm looked nothing like a tornado, so the question arises, 'Would the public take cover?' The most important thing to protecting your life is to listen to the weather reports. When a tornado warning is issued for your area, it is important to take cover immediately.