tornadoes - yolalwcmeteorology.yolasite.com/resources/ch 10 - tornadoes.pdf · tornado facts • 2....
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Tornadoes Be able to define what a tornado is.
Be able to list several facts about tornadoes.
1. Where do tornadoes most
occur in the world? • U.S. is # 1
• Tornadoes are most common in “Tornado Alley.”
Tornado Facts • 2. 1000 tornadoes spin up beneath
T-Storms each year in the U.S. – 1,253 tornadoes per year in the U.S.
• 3. Typically kill about 60 – 80 people
• 4. Tornadoes are violently rotating
columns of air attached to a
thunderstorm and in contact with the
ground, whether or not a
condensation funnel is visible to the
ground.
– Stronger pressure gradient than a
hurricane.
2013 Tornado Data
5. Where have tornadoes occurred?
• Tornadoes have occurred:
– In all 50 States
– On all continents except Antarctica
6a. When do most tornadoes occur?
• April to July
• During late spring to early summer.
6b. When do most tornadoes occur?
• 2 pm to 8 pm
• During afternoon and evening hours
7. What forward speed do tornadoes
move at?
• The average forward speed is 30mph but may vary from nearly stationary to 70mph
8. Where does a tornado come from?
• It’s called a funnel cloud until it makes contact with the ground.
• A cloud that protrudes below the cloud base is called the wall cloud. – Updraft of the storm
9. How do Tornadoes look? • Tornadoes take different forms, some are large and
ominous, while others are relatively small and may be difficult to see.
Tornado Variations in Appearance
• Pencil-shaped tornado about the time of F5
damage near Union City, OK, May 24,1973.
Tornado Variations in Appearance
• Cone-shaped tornado with debris fan south of
Hill City, KS, looking west, June 9, 2005.
Tornado Variations in Appearance
• “Wedge” tornado, where the visible funnel is wider than
the distance from ground to surrounding cloud base,
looking northwest near Argonia, KS, May 29, 2004.
10. What is a Waterspout • Waterspouts are tornadoes that occur over water.
– Two types of water spouts
• Type A waterspout forms in thunderstorm and travels over water (More
violent)
• Type B waterspout forms from building cumulus clouds (less violent)
– If this forms on land it is called a landspout
1950 – 2006 Tornado Tracks
11. Tornadoes usually move in which direction?
• Tornadoes can appear from
any direction. Most move
from southwest to
northeast.
• Most tornadoes -- but not
all! -- rotate cyclonically, (which is counterclockwise in the N.H.)
12. What scale is used to measure tornado strength?
Fujita Scale – Because tornado winds cannot be measured directly,
a rating on the Fujita scale is determined by assessing the worst damage produced by the storm.
Fujita Scale
• F0 (40-72 mph) – Light damage. Some damage to chimneys; branches broken off trees; shallow-rooted trees
pushed over; sign boards damaged.
• F1 (73-112 mph) – Moderate damage. The lower limit is the beginning of hurricane wind speed; surface peeled
off roofs; mobile homes pushed off foundations or overturned; moving autos pushed off the roads.
• F2 (113-157 mph) – Considerable damage. Roofs torn off frame houses; mobile homes demolished; boxcars
pushed over; large trees snapped or uprooted; light-object missiles generated.
• F3 (158-206 mph) – Severe damage. Roofs and some walls torn off well-constructed houses; trains overturned;
most trees in forest uprooted; heavy cars lifted off ground and thrown.
• F4 (207-260 mph) – Devastating damage. Well-constructed houses leveled; structures with weak foundations
blown some distance; cars thrown and large missiles generated.
• F5 (261-318 mph) – Incredible damage. Strong frame houses lifted off foundations and carried considerable
distances; automobile sized missiles thrown through the air in excess of 100 yd (equivalent to 91 m); trees debarked.
13. How do Tornadoes Form?
Need Wind Shear
• A change in wind direction
and an increase in wind
speed with increasing height
– creates an invisible, horizontal
spinning effect in the lower
atmosphere.
– Rising air within the
thunderstorm's updraft tilts the
rotating air from horizontal to
vertical.
Tornado Formation
Weak Tornadoes F0-F1
• 69% of all tornadoes
• Less than 5% of
tornado deaths
• Lifetime 1-10+
minutes
• Winds less than 110
mph
Strong Tornadoes F2-F3
• 29% of all tornadoes
• Nearly 30% of all
tornado deaths
• May last 20 minutes or
longer
• Winds 110-205 mph
Violent Tornadoes F4-F5
• Only 2% of all
tornadoes
• 70% of all tornado
deaths
• Lifetime can exceed 1
hour
• Winds greater than 205
mph
Environmental Clues
• Tornadoes are often preceded by a dark, often greenish sky, large hail, and often a loud roar, similar to a freight train.
• Most strong and violent tornadoes occur with "supercell" thunderstorms.
Remember Other Threats
• In addition to tornadoes, thunderstorms often produce other hazards.
• Flash Floods/Floods – The number ONE thunderstorm-related killer -- averages 146
deaths annually.
• Lightning – Kills 75 to 100 people each year
• Damaging Straight-Line Winds – Can reach speeds of 140 mph
• Large Hail – Often the size of golf balls and occasionally can reach grapefruit
size. Hail causes several hundred million dollars in damage annually to property and crops.
Tornado Watch
• Tornado Watch
– alert people to the possibility of tornadoes in a
specified area for a particular time.
Tornado Warning • Tornado Warning
– A tornado warning is issued when a tornado has actually been sighted in an area or is indicated by weather radar.
– With new technology we have gone from 5 minutes to 15 minutes of warning time for tornadoes
Radar Tornadoes (J-Hook)
Tornado Safety
• If you are caught outdoors, seek shelter in a
basement, shelter or sturdy building.
• If you cannot quickly get to a shelter,
immediately get into a vehicle, buckle your seat
belt and try to drive to the closest sturdy shelter.
• If flying debris occurs while you are driving, pull
over and park. You have the following options as
a last resort:
Tornado Safety
• Stay in the car with the seat belt on. Put
your head down below the windows,
covering with your hands or a blanket if
possible.
• If you can safely get noticeably lower than
the level of the roadway, exit your car, and
lie in that area, covering your head with your
hands.
Tornado Safety
• Flying and falling debris is the biggest hazard in
a tornado. To be safe, you should get inside, get
down and cover up. Underground or in a Safe
Room is your first choice. If no underground
shelter is available, get to the center of a sturdy
building on the lowest level. Put as many walls
between you and the tornado as possible. Stay
away from windows and doors. Cover up to help
minimize being injured by flying or falling debris.