Nature's Most Violent Storms
A PREPAREDNESS GUIDE
Including Safety Information for Schools
U.S. DEPARTMENT OF COMMERCE
National Oceanic and Atmospheric Administration
National Weather Service
NOAA,FEMA,American Red Cross
Although tornadoes occur in many parts of
the world, these destructive forces of nature
are found most frequently in the United States
east of the Rocky Mountains during the
spring and summer months. In an average
year, 800 tornados are reported nationwide,
resulting in 80 deaths and over 1,500 injuries.
A tornado is defined as a violently rotating
column of air extending from a thunderstorm
to the ground. The most violent tornadoes are
capable of tremendous destruction with wind
speeds of 250 mph or more. Damage paths
can be in excess of one mile wide and 50
miles long. Once a tornado in Broken Bow,
Oklahoma, carried a motel sign 30 miles and
dropped it in Arkansas!
What causes tornadoes?
Thunderstorms develop in warm, moist air
in advance of eastward-moving cold fronts.
These thunderstorms often produce large
hail, strong winds, and tornadoes.
Tornadoes in the winter and early spring
are often associated with strong, frontal
systems that form in the Central States and
move east. Occasionally, large outbreaks
of tornadoes occur with this type of
weather pattern. Several states may be
affected by numerous severe
thunderstorms and tornadoes.
During the spring in the Central Plains,
thunderstorms frequently develop along a
"dryline," which separates very warm,
moist air to the east from hot, dry air to the
west. Tornado-producing thunderstorms
may form as the dryline moves east during
the aftemoon hours.
Along the front range of the Rocky
Mountains, in the Texas panhandle, and in
the southern High Plains, thunderstorms
frequently form as air near the ground
flows "upslope" toward higher terrain. If
other favorable conditions exist, these
thunderstorms can produce tornadoes.
Tornadoes occasionally accompany
tropical storms and hurricanes that move
over land. Tornadoes are most common to
the right and ahead of the path of the storm
center as it comes onshore.
* Some tornadoes may form during
the early stages of rapidly
developing thunderstorms. This
type of tornado is most common
along the front range of the Rocky
Mountains, the Plains, and the
* Tornadoes may appear nearly
transparent until dust and debris
are picked up.
* Occasionally, two or more
tornadoes may occur at the same
* Waterspouts are weak tornadoes that form over
* Waterspouts are most common along the Gulf Coast
and southeastern states. In the western United
States, they occur with cold late fall or late winter
storms, during a time when you least expect
* Waterspouts occasionally move inland becoming
tornadoes causing damage and injuries.
How Do Tornadoes Form?
Before thunderstorms develop, 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 updraft tilts the
rotating air from horizontal to
An area of rotation, 2-6 miles wide, now extends
through much of the storm. Most strong and violent
tornadoes form within this area of strong rotation.
This area of rotation known as a rotating wall cloud is often
Moments later a strong tornado develops in this area.
Softball-size hail and damaging "straight-line" winds
may also occur.
TORNADOES TAKE MANY SHAPES AND SIZES
* 69% of all tornadoes
* Less than 5% of tornado deaths
* Lifetime 1-10+ minutes
* Winds less than 100 mph
* 29% of all tornadoes
* Nearly 30% of all tornado deaths
* May last 20 minutes or longer
* Winds 110-205 mph
* Only 2% of all tornadoes
* 70% of all tornado deaths
* Lifetime can exceed 1 hour
* Winds greater than 205 mph
MYTH: Areas near rivers, lakes, and mountains are safe from
FACT: No place is safe from tornadoes. In the late 1980's, a
tornado swept through Yellowstone National Park leaving a path of
destruction up and down a 10,000 ft. mountain.
MYTH: The low pressure with a tornado causes buildings to
"explode" as the tornado passes overhead.
FACT: Violent winds and debris slamming into buildings cause most
MYTH: Windows should be opened before a tornado approaches to
equalize pressure and minimize damage.
FACT: Opening windows allows damaging winds to enter the
structure. Leave the windows alone; instead, immediately go to a
TORNADOES OCCUR ANYWHERE
* March 28, 1984,
* 22 tornadoes
* 57 deaths
* 1,248 injuries
* damage $200 million
* 37% of fatalities in mobile
* May 31, 1985, late
* 41 tornadoes, including 27 in
PA and OH
* 75 deaths in U.S.
* l,025 injuries
* damage $450 million
* April 26-27, 1991, afternoon
of 26th through early morning 27th
* 54 tornadoes
* 21 deaths
* 308 injuries
* damage $277+ million
* 15 deaths in/near mobile homes,
2 deaths in vehicles
Weather Radar Watches the Sky
Meteorologists rely on weather radar to provide infor-
mation on developing storms. The National Weather
Service is strategically locating Doppler radars across
the country which can detect air movement toward or
away from the radar. Early detection of increasing
rotation aloft within a thunderstorm can allow life-
saving warnings to be issued before the tornado forms.
In the figure below left, Weather Service Doppler radar
detects strong rotation within the storm where red
colors (winds moving away from the radar) and green
colors (winds blowing toward the radar) are close
together. The photograph at lower right shows a
violent tornado in northern Oklahoma at the same time
the radar image was taken.
Frequency of Tornadoes
* In the southern states, peak tornado
occurrence is in March through May,
while peak months in the northern
states are during the summer.
* Note, in some states, a secondary
tornado maximum occurs in the fall.
* Tornadoes are most likely to occur
between 3 and 9 p.m. but have been
known to occur at all hours of the day
* The average tornado moves from
southwest to northeast, but tornadoes
have been known to move in any
direction. The average forward speed
is 30 mph but may vary from nearly
stationary to 70 mph.
* The total number of tornadoes is
probably higher than indicated in the
western states. Sparce population
reduces the number reported.
STAY INFORMED ABOUT THE STORM by listening to NOAA Weather Radio,
commercial radio, and television for the latest tornado WATCHES
When conditions are favorable for severe weather to
develop, a severe thunderstorm or tornado WATCH
Severe thunderstorm warnings are passed to local radio and tele-
vision stations and are broadcast over local NOAA Weather Radio
stations serving the warned areas. These warnings are also
relayed to local emergency management and public safety officials
who can activate local warning systems to alert communities.
NOAA WEATHER RADIO IS THE BEST MEANS TO RECEIVE WARNINGS
FROM THE NATIONAL WEATHER SERVICE
The National Weather Service continuously broadcasts updated
weather warnings and forecasts that can be received by NOAA
Weather Radios sold in many stores. The average range is 40
miles, depending on topography. Your National Weather Service
recommends purchasing a radio that has both a battery backup and
a tone-alert feature which automatically alerts you when a watch
or warning is issued.
What To Listen For...
TORNADO WATCH: Tornadoes are possible in your area. Remain alert
for approaching storms.
TORNADO WARNING: A tornado has been sighted or indicated by
weather radar. If a tornado warning is issued for your area and
the sky becomes threatening, move to your pre-designated
place of safety.
SEVERE THUNDERSTORM WATCH: Severe thunderstorms are possible in
SEVERE THUNDERSTORM WARNING: Severe thunderstorms are occurring.
Remember, tornadoes occasionally develop in areas
in which a severe thunderstorm watch or warning is in effect.
Remain alert to signs of an approaching tornado and
seek shelter if threatening conditions exist.
Look out for:
* Dark, often greenish sky * Large hail * Wall cloud * Loud
roar, similar to a freight train
* Some tornadoes appear as a visible funnel
extending only partially to the ground. Look
for signs of debris below the visible funnel.
* Some tornadoes are clearly visible while
others are obscured by rain or nearby
OTHER THUNDERSTORM HAZARDS
These dangers of ten
* Flash Floods: Number ONE weather killer-146 deaths annually
* Lightning: Kills 75-100 people each year
* Damaging straight-line winds Can reach 140mph
* Large Hail: Can reach the size of a grapefruit-causes
several hundred million dollars in damage
annually to property and crops
Contact your local National Weather Service office, American
Red Cross chapter, or Federal Emergency Management Agency
office for a copy of the "Thunderstorms and Lightning...The
Underrated Killers" brochure (NOAA PA 92053) and the
"Flash Floods and Floods...The Awesome Power" brochure
(NOAA PA 92050).
What YOU Can Do
Before the Storm:
* Develop a plan for you and your family for home,
work, school, and when outdoors.
* Have a NOAA Weather Radio with a warning alarm tone and battery
back-up to receive warnings.
* Have frequent drills.
* Listen to radio and television for information.
* Know the county/parish in which you live, and
keep a highway map nearby to follow storm movement from weather
* If planning a trip outdoors, listen to the latest
forecasts and take necessary action if threatening
weather is possible.
If a Warning is issued or if
threatening weather approaches:
* In a home or building, move to a pre-designated shelter,
such as a basement.
* If an underground shelter is not available, move to an
interior room or hallway on the lowest floor and get
under a sturdy piece of furniture.
* Stay away from windows.
* Get out of automobiles.
* Do not try to outrun a tornado in your car; instead, leave
* If caught outside or in a vehicle, lie flat in a nearby ditch
* Mobile homes, even if tied down, offer little protection
from tornadoes and should be abandoned.
Occasionally, tornadoes develop so rapidly that advance
warning is not possible. Remain alert for signs of an
approaching tornado. Flying debris from tornadoes
causes most deaths and injuries.
It's Up To YOU!
Each year, many people are killed or seriously injured by
tornadoes despite advance warning. Some did not hear the warning
while others received the warning but did not believe a tornado
would actually affect them.
The preparedness information in this brochure, combined with
timely severe weather watches and warnings,could save your life
in the event a tornado threatens your area. After you have
received the waming or observed threatening skies, YOU must make
the decision to seek shelter before the storm arrives. It could
be the most important decision you will ever make.
Who's Most At Risk?
* People in automobiles * People in mobile homes
* The elderly, very young, and the physically or mentally
* People who may not understand the warning due to a language
TORNADO SAFETY IN SCHOOLS
EVERY School Should Have A Plan!
* Develop a severe weather action plan and have
* Each school should be inspected and tomado shelter
areas designated by a registered engineer or architect.
Basements offer the best protection. Schools without
basements should use interior rooms and hallways on
the lowest floor and away from windows.
* Those responsible for activating the plan should
monitor weather information from NOAA Weather
Radio and local radio/television.
* If the school's alarm system relies on electricity, have
a compressed air horn or megaphone to activate the
alarm in case of power failure.
* Make special provisions for disabled students and
those in portable classrooms.
* Make sure someone knows how to turn off electricity
and gas in the event the school is damaged.
* Keep children at school beyond regular hours if
threatening weather is expected. Children are safer at
school than in a bus or car. Students should not be
sent home early if severe weather is approaching. Lunches
or assemblies in large rooms should be
delayed if severe weather is anticipated.
Gymnasiums, cafeterias, and auditoriums offer no
protection from tornado-strength winds.
* Move students quickly into interior rooms or
hallways on the lowest floor. Have them assume the
tornado protection position .
Hospitals, nursing homes, and other institutions should develop a
Your National Weather Service, Federal Emergency Management
Agency, and American Red Cross educate community officials and
the public concerning the dangers posed by tornadoes. YOU can
prepare for the possibility of a tornado by learning the safest
places to seek shelter when at home, work, school, or outdoors.
You should also understand basic weather terms and danger signs
related to tornadoes. Your chances of staying safe during a
tornado are greater if you have a plan for you and your
family, and practice the plan frequently.
FAMILY DISASTER PLAN
Families should be prepared for all hazards that affect their
area. NOAA's National Weather Service, the Federal Emergency
Management Agency, and the American Red Cross urge each family to
develop a family disaster plan.
Where will your family be when disaster strikes? They could be
anywhere - at work, at school, or in the car.
How will you find each other? Will you know if your children are
safe? Disasters may force you to evacuate your neighborhood or
confine you to your home. What would you do if basic services -
water, gas,electricity or telephones - were cut off?
Follow these basic steps to develop a family disaster plan...
I. Gather information about hazards. Contact your local National
Weather Service office, emergency management or civil defense
office, and American Red Cross chapter. Find out what type of
disasters could occur and how you should respond. Learn your
community's warning signals and evacuation plans.
II. Meet with your familv to create a plan. Discuss the
information you have gathered. Pick two places to meet:
a spot outside your home for an emergency, such as fire, and a
place away from your neighborhood in case you can't return home.
Choose an out-of-state friend as your "family check-in contact"
for everyone to call if the family gets separated. Discuss what
you would do if advised to evacuate.
III. Implement your plan. (1) Post emergency telephone numbers
by phones; (2) Install safety features in your house, such as
smoke detectors and fire extinguishers; (3) Inspect your home for
potential hazards (such as items that can move, fall, break, or
catch fire) and correct them; (4) Have your family learn basic
safety measures, such as CPR and first aid; how to use a fire
extinguisher; and how and when to turn off water, gas, and
electricity in your home; (5) Teach children how and when to call
911 or your local Emergency Medical Services number; (6) Keep
enough supplies in your home to meet your needs for at least
three days. Assemble a disaster supplies kit with items you may
need in case of an evacuation.Store these supplies in sturdy,
easy-to-carry containers, such as backpacks or duffle bags. Keep
important family documents in a waterproof container. Keep a
smaller disaster supplies kit in the trunk of your car.
A DISASTER SUPPLIES KIT SHOULD INCLUDE:
A 3-day supply of water (one gallon per person per day) and food
that won't spoil * one change of clothing and footwear per person
* one blanket or sleeping bag per person * a first-aid kit,
including prescription medicines * emergency tools, including a
battery-powered NOAA Weather Radio and a portable radio,
flashlight, and plenty of extra batteries * an extra set of car
keys and a credit card or cash * special items for infants,
elderly, or disabled family members.
IV, Practice and maintain your plan. Ask questions to make sure
your family remembers meeting places, phone numbers, and safety
rules. Conduct drills. Test your smoke detectors monthly and
change the batteries at least once a year. Test and recharge your
fire extinguisher(s) according to manufacturer' s instructions.
Replace stored water and food every six months.