Tornadoes
Chapter 17
Sections 2 & 3
Pages 567-582
Tornadoes
• A rapidly whirling, funnel-shaped cloud
that reaches down from a storm cloud to
touch Earth’s surface.
– Usually are on the ground for 15 min or less.
– May be only a few hundred meters across
– Wind speeds approach 480km/hr (300mph)
• If it occurs over a lake or ocean, it is called
a water spout.
How Tornadoes Form
• Develop in low, heavy cumulonimbus
clouds.
• Most likely during spring and early
summer, often late in the afternoon.
How Tornadoes Form
• Tornado Alley- located in the great plains.
– Cold, dry air moves south from Canada.
– Warm, humid air moves north from the Gulf.
– Causes a squall line of thunderstorms to form
which are severe.
– US averages 800 tornadoes a year.
Fujita Scale
Category
F-Scale
Estimated Wind
Speed km/h
Estimated Wind
Speed mph
F0
65-118 km/h
40-72 mph
Minor damage, snaps small
branches, breaks some
windows
F1
119-181 km/h
73-112 mph
Downs trees, shifts mobile homes
off foundations
Weak
Strong
Violent
Effects
F2
182-253 km/h
113-157 mph
Rips roofs off houses, destroys
mobile homes, uproots large
trees
F3
254-332 km/h
158-206 mph
Partially destroys buildings, lifts
cars
F4
333-419 km/h
207-260 mph
F5
420-513 km/h
261-318 mph
Levels sturdy buildings, tosses cars
Lifts and transports sturdy
buildings
Tornado Safety
• Damage is due to strong winds and flying
debris (objects picked up by the tornado)
• The low pressure sucks up dust and other
objects into the funnel.
• Tornadoes can move large objects.
– Sheds
– Trailers
– Cars
– Homes
Tornado Safety
• Tornado Watch- possible tornadoes are in
your area.
• Tornado Warning- a tornado has been
spotted on the ground.
Tornado Safety
• The safest place to be is in the basement
of a well built building.
• If no basement, move to the middle of the
ground floor. (typically a bathroom)
– Stay away from windows and doors.
– Lie on the floor under a sturdy type of
furniture (a large table)
Tornado Safety
• If in a mobile home or a car, move to a
building or lie flat in a ditch.
– Underpasses are NOT safe places to seek
shelter.
Storm
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