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Earth Science  Explain why some are more severe than others

 Recognize the dangers of severe , including , , and high winds

 Describe how tornadoes form  Some thunderstorms may last a few minutes while others can go longer  What makes one more severe than another?

 The increasing instability of the air intensifies the strength of a ’s updrafts and downdrafts, which makes the storm severe  Severe thunderstorms can develop into self- sustaining, extremely powerful called  These furious storms can last for several hours and can have updrafts as strong as 240 km/h  Characterized by an anvil- shaped cumulonimbus

 Very few reach the severe stage  RECALL: -cooled downdrafts descend to Earth’s surface during a , where they spread out as they reach the ground  Sometimes these may be concentrated in a local area and can be exceptionally strong  Known as

 Based on the size of the area they affect, downbursts are classified as either macrobursts or microbursts

 Each year in the United States, almost one billion dollars in damage is caused by hail

 Hail forms because of two characteristics common to thunderstorms 1. Water droplets rise to the heights of a where the temperature is below freezing, encounter pellets, and freeze on contact with the pellets, which causes the ice pellets to grow larger 2. An abundance of strong updrafts and downdrafts moving side by side within a cloud

 A is a violent, whirling column of air IN CONTACT w/ the ground  Before it reaches the ground, we have a funnel cloud

 The air in a tornado is made visible by dust and debris drawn into the swirling column, or by the condensation of water vapor into a visible cloud  A tornado forms when wind speed and direction change suddenly w/ height  Current thinking suggest that tornadoes form when small pockets of cooler air are given a horizontal, rolling-pin type of rotation  If this occurs close enough to the thunderstorm’s updrafts, the twisting column of wind can be tilted from a horizontal to a vertical position  As updrafts stretch the column, the rotation is accelerated  Air is removed from the center of the column, which in turn lowers the air pressure in the center  This pressure gradient produces the violent winds of tornadoes

 Tornadoes are categorized according to their destructive force  The Fujita tornado intensity scale, which ranks tornadoes according to their path of destruction, wind speed, and duration, is used to classify tornadoes  Goes from F0 to F5  Enhanced Fujita scale implemented in 2007  Revised to better reflect tornado damage  80 percent of all  http://youtu.be/1a3- tornadoes Cy6UWc8

 Damage path of up to 4 km

 Usually last 1-10 minutes  http://youtu.be/LT4Gg8 RtaKs  Wind speed: 70-180 km/h (65-110 mph)  19 percent of all  http://youtu.be/Jo8il_Kg tornadoes _j8

 Damage path of 24+ km

 Duration of 20+ min  http://youtu.be/mZI87w Fcqwg  Wind speeds between 181-332 km/h (111-165 mph)  1 percent of all tornadoes  http://youtu.be/mor4bN x0QGQ  Damage path of 80+ km

 Duration of 1+ hours  http://youtu.be/eQcBcS  Wind speed: 333-512+ VKb6U km/h (166-200+ mph)   http://youtu.be/hVgKQj us-FQ  Snowspout  http://youtu.be/E9vZn TJHqzQ  Fire tornadoes

 http://youtu.be/lsyvO YcWgcg

 http://youtu.be/JaSZFu p_y94  Most tornadoes—especially violent ones—form in the during the late afternoon and evening, when the temperature contrasts between polar air and tropical air are the greatest  This type of large temperature contrast occurs most frequently in the central United States  Many of the more than 700 tornadoes that touch down in the United States each year occur in a region called “Tornado Alley,” which extends from northern Texas through Oklahoma, Kansas, and Missouri  If you are caught in a tornado, take shelter in the southwest corner of a basement, a small downstairs room or closet, or a tornado shelter  Reading:  None  Video

 Homework:  pg. 354 (1-8)