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Weather Patterns & Severe StormsCh. 20 sec. 3 only
200
• What is a tornado?– violently rotating column of air• usually touches the ground
• What do tornadoes look like?–often vortex or funnel-shaped
cloud (w/ flying debris)– can also be:• rope shaped• wedge shaped–w/ more than one vortex
Tornadoes
• How do tornadoes form?– rotating updraft forms
(mesocyclone)– air pressure at center = very low• air sucked in expands & cools–water vapor condenses & wall cloud
may become visible @ base of storm
• If air is drier or pressure is higher, cloud may contain dust & debris– creates loud roaring sound
TornadoesBrain Pop: Tornadoes
• When & where do tornadoes form?–anywhere & at any time of year•MOSTLY in “Tornado Alley” (Texas northward
to South Dakota) in spring & early summer
Tornadoes
• How is the intensity of a tornado measured?– Fujita scale• F0 (weakest) to F5 (most violent)
• What are the effects of tornadoes?
Tornadoes
Tornadoes• Predicting formation & path is difficult.–Why?• b/c destructive & often unpredictable–can damage instruments–can put people in danger
–Improvements have been made.• conventional radar map precipitation• Doppler radar identify which way winds are
moving within storm–can identify a rotating mesocyclone & give people
~20 min advance warning
Tornadoes• What is the difference between a tornado
watch & warning?–watch tornado MAY form–warning tornado spotted
• What is the difference between a hurricane, typhoon, & cyclone?–location•Atlantic–hurricane
•Pacific–typhoon
• Indian–cyclone
Hurricanes
Hurricanes• What is a hurricane?– a large rotating storm of tropical origin that has
sustained winds of at least 119 km/hr (74 mph)
Hurricanes• How do hurricanes form?– in tropics a mild atmospheric disturbance causes
humid air to rise• more water condenses & releases heat– continues as long as humid air is available & rising
» to become a hurricane, it must begin to rotate (counterclockwise in the N. Hemi. due to Coriolis Effect)
Animated Guide: HurricaneBrain Pop: Hurricanes
Hurricanes• What are the 3 main parts of a hurricane?–eye• lowest pressure– calm
–eye wall• outer edge of eye• strongest wind• strongest rain
– rain bands• clouds that spin out• make storm bigger
Hurricanes• What is the
pressure like at the center of a hurricane?– very low
• Hurricane Sandy– lowest pressure
for any storm to hit north of North Carolina• 940 millibars or
27.76 inches
• What determines the path of a hurricane?– global wind patterns• In Atlantic (N. Hemi.) generally move west or northwest.
– Then, often curve north (and may eventually head east).
– actual paths can vary considerably… • shown by “cone of uncertainty”
Hurricanes
• What are some of the effects of hurricanes?–wind damage– inland flooding– storm surge• large wave of
water from strong winds of eye wall– blow water
into a dome
–waves• coastal erosion
Hurricanes
• When is hurricane season in the U. S.?– June 1 – November 30
• Difference between hurricane watch & warning?–watch expected to arrive w/in 24-36 hours–warning expected to w/in 24 hours or less
Hurricanes
• How do scientists classify tropical storms/hurricanes?–by wind speed• tropical depression up to 61 km/hr• tropical storm 61
– 119 km/hr• hurricane 119+
km/hr– Saffir-Simpson scale
to rate strength
Hurricanes