16 - GEOL 0820 Ramsey Natural Disasters Spring, 2011...

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GEOL 0820 Ramsey Natural Disasters Spring, 2011 LECTURE #16: Severe Weather: Tornadoes Date: 17 March 2011 I. Tornado General Information generated in regions of already severe thunderstorms two prime factors for tornado initiation o topography o local climate created over areas undisturbed by mountains o very common in midwestern US ± "tornado alley" (TX, OK, KS, NB, IA) o only Alaska has not experienced a tornadoes II. Formation average dimensions o width: 75 yards o track length: 1-4 miles o time on ground: 5 min. o forward speed: 25 mph Page 1/7
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timing o prime season for this combination ± spring-summer o prime time of day ± late afternoon -- late evening ± time of maximum local ground heating JAN JUL FEB AUG MAR SEP APR OCT Page 2/7
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MAY NOV JUN DEC structure o combination of opposing wind patterns ± high level, relatively dry/cooler winds from the west ± lower level, warm/wet winds from the east ¾ originating in the Gulf of Mexico o winds form cyclonic rotation parallel to the ground (rollers) o large thunderstorms pull warmer air upward from low levels ± warm/wet air provides energy for the storm o large updrafts can cause a roller to tip into a vertical position o tornado is born upon touchdown with the ground
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This note was uploaded on 01/05/2012 for the course GEOL 0820 taught by Professor Ramsay during the Spring '08 term at Pittsburgh.

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16 - GEOL 0820 Ramsey Natural Disasters Spring, 2011...

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