National Geographic : 2013 Nov
Cool downdraft Overshooting top Upper-level winds and direction of storm Warm updraft TORNADO TORNADOALLEY Cold, dry air Warm, moist air Gulf of Mexico ROCKYMOUNTAINS Warm, dry air Jetstream UNITED STATES The “cap” between air masses temporarily prevents thunderstorm formation. Less dense air wants to rise. Heaviest air wants to sink. Up to 45,000 feet 6,000 3,000 Wall cloud 2 to 3 miles wide Precipitation Mesocyclone The rising warm, moist air forms clouds as it cools and condenses. Only a fraction of supercells (rotating thunderstorms) produce tornadoes. 2 3 4 1 0mi 200 0km 200 ROCKYMOUNTAINS MINN. COLO. ARK. IOWA KANS. MO. NEBR. S. DAK. LA. TEX. FLA. GA. MISS. ALA. ILL. IND. KY. OHIO TENN. VA. N.J. CONN. MASS. N.C. S.C . WIS. PA. MD. MICH. OKLA. Denver Bennett Manchester Moore Oklahoma City El Reno Where twisters strike tornadoes 1950-2013, rated1to5onthe enhanced fujita (ef) scale* low tornado occurrence single tornado track high suPerCell upper-level winds tilt the rotating updraft, called a mesocyclone. this allows the storm to keep growing, as warm air is sucked into the storm away from the cool downdraft. At 5:26 p.m. a tornado warning is issued. At 6:03 a funnel touches down southwest of El Reno. The El Reno tornado formed chaotically, with dozens of small vortices that combined at times to form one large one. The vortices developed on different scales, some as narrow as cars, others wider than a football field.