Weather Patterns & Severe StormsCh. 20 sec. 3 only

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• 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