GEOS 110
NATURAL DISASTERS
 
Tornadoes-I
Intro
 - Most violent and intense storms on Earth- but only affect a small area; total    energy release is small. Responsible for ~150 deaths per year and millions in    property damage. Usual destruction of property is total.
 
How a Tornado Works
 - Associated with strong thunderstorms that develop when 3 main atmospheric   conditions occur simultaneously in the central US
   1) a northerly flow of warm, moist air from the Gulf of Mexico
   2) a cold, dry air mass rapidly moving southward from Canada or the      Rocky Mtns (>50 mph).
   3) strong easterly jet stream (>150 mph)
 - These three air masses moving in different directions produce shearing     conditions that are give thunderstorm clouds a "spin"
 - Funnel clouds begin to form, they may (or may not) touch down and develop in   to a tornado.
 
Tornado Characteristics
 - About 70% of all tornadoes on Earth occur in the central and southern US.
   "Tornado Alley" - Northen Texas and Oklahoma
 - Occur mostly in late spring - early summer when conditions are best for tornado   formation; but can occur anytime.
 - Can move at speeds up to ~60 mph and have max wind speeds of >300 mph.
 - They cause a narrow damage track of a few hundred feet to ~1 wide. Usually less   than about ~10 miles long.
- Tornado "magnitude" measured on the Fujita Scale (F0-F5); based on wind   speed