Tornadoes....
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 September 1992 (NOAA, FEMA, The American Red Cross )
Tornado!
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
tornadoes 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 afternoon 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.
Tornado Variations
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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 Western States.
Tornadoes may appear nearly transparent until dust and debris are picked up.
Occasionally, two or more tornadoes may occur at the same time.
Waterspout
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Waterspouts are weak tornadoes that form over warm water.
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 tornado development.
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 vertical.
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.
A lower cloud base in the center of the photograph identifies an area of rotation known as a rotating wall cloud. This
area is often nearly rain-free. Note rain in the background.
Moments later a strong tornado develops in this area. Softball-size hail and damaging "straight-line" winds also
occurred with this storm.
Tornadoes Take Many
Shapes and Sizes
Weak Tornadoes
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69% of all tornadoes
Less than 5% of tornado deaths
Lifetime 1-10+ minutes
Winds less than 110 mph
Strong Tornadoes
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29% of all tornadoes
Nearly 30% of all tornado deaths
May last 20 minutes or longer
Winds 110-205 mph
Violent Tornadoes
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Only 2% of all tornadoes
70% of all tornado deaths
Lifetime can exceed 1 hour
Winds greater than 205 mph
Tornado Myths:
MYTH: Areas near rivers, lakes, and mountains are safe from tornadoes.
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 structural damage.
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 safe place.
Tornadoes Occur Anywhere
Carolinas Outbreak:
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March 28, 1984, afternoon-evening
22 tornadoes
57 deaths
1,248 injuries
damage $200 million
37% of fatalities in mobile homes
Pennsylvania-Ohio Outbreak:
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May 31, 1985, late afternoon-evening
41 tornadoes, including 27 in PA and OH
75 deaths in U.S.
1,025 injuries
damage $450 million
Plains Outbreak:
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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 information 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.
Frequency of Tornadoes
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Tornadoes can occur at any time of the year.
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 or night.
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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. Sparse 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
and WARNINGS.
When conditions are favorable for severe weather to develop, a severe thunderstorm or tornado WATCH is issued.
Weather Service personnel use information from weather radar, spotters, and other sources to issue severe
thunderstorm and tornado WARNINGS for areas where severe weather is imminent.
Severe thunderstorm warnings are passed to local radio and television 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 your area.
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.
Environmental Clues
Look out for:
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Dark, often greenish sky
Wall cloud
Large hail
Loud roar; similar to a freight train
Caution:
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 low-hanging clouds.
Other Thunderstorm Hazards
These dangers often accompany thunderstorms:
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Flash Floods: Number ONE weather killer - 146 deaths annually
Lightning: Kills 75-100 people each year
Damaging Straight-line Winds: Can reach 140 mph
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).
Tornado Safety
What YOU Can Do
Before the Storm:
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Develop a plan for you and your family for home, work, , school and when outdoors.
Have frequent drills.
Know the county/parish in which you live, and keep a highway map nearby to follow storm movement from
weather bulletins.
Have a NOAA Weather Radio with a warning alarm tone and battery back-up to receive warnings.
Listen to radio and television for information.
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:
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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.
If you are caught outdoors, seek shelter in a basement, shelter or sturdy building. If you cannot quickly walk
to a shelter:
o Immediately get into a vehicle, buckle your seat belt and try to drive to the closest sturdy shelter.
o If flying debris hits your vehicle while you are driving, pull over and park.
Now you have the following options as a last resort:
Stay in the car with the seat belt on. Put your head down below the windows, covering with your
hands and a blanket if possible.
o 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.
o Your choice should be driven by your specific circumstances.
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.
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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 warning 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?
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People in mobile homes
The elderly, very young, and the physically or mentally impaired
People who may not understand the warning due to a language barrier
People in an unfamiliar place such as tourists
People that are outdoors
Tornado Safety in Schools
EVERY School Should Have A Plan!
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Develop a severe weather action plan and have frequent drills,
Each school should be inspected and tornado 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 (shown at right).
Hospitals, nursing homes, and other institutions should develop a
similar plan
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 family 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:
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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 infant, 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.
DESCRIPTION OF HISTORICAL EVENTS
RELATING TO TORNADO FORECASTING IN THE LATE 1940s AND EARLY
1950s.
Transcribed by Charlie A. Crisp from parts of the unpublished manuscript (written
middle to late 1970S),
THE UNFRIENDLY SKY
WRITTEN BY
ROBERT C. MILLER
Colonel, USAF-Ret
A PLEA FOR UNDERSTANDING
The close knit world of the tornado and severe thunderstorm forecaster often seems
somewhat demented to those not knowledgeable in this discipline. This apparent
derangement is based on our seemingly ghoulish expressions of joy and satisfaction
displayed whenever we verify a tornado forecast. This aberration is not vicious;
tornadoes in open fields make us happier than damaging storms and count just as
much for or against us. We beg your indulgence, but point out the sad truism that we
rise and fall by the blessed verification numbers. There is a fantastic feeling of
accomplishment when a tornado forecast is successful. We are really nice people but
odd.
ROBERT C. MILLER, Colonel, USAF-Ret
EVENTS LEADING TO THE FIRST
OPERATIONAL TORNADO FORECAST
IN THE WORDS OF
ROBERT C. MILLER
Colonel, USAF-Ret
March 20, 1948
I was assigned forecasting duty in the Tinker Air Force Base Weather Station, under
the command of Major J. Fawbush, on the first of March 1948. The evening of March
20th, while on the evening shift, I was rudely awakened to the sometimes vicious
vagaries of Mother Nature. There were two of us on shift that night. My backup
forecaster was a Staff Sergeant, also new to the Tinker Weather Station. In course of
idle conversation we found we had much in common - we were both from Sunny
Southern California and had no weather experience in the Midwest portion of the
United States. We analyzed the latest surface weather maps and upper charts and
arrived at the same conclusion that except for moderately gusty surface winds, we
were in for a dry and dull night. We were not astute enough to note that the upper-air
analyses, received in completed form over the facsimile net from the USWB in
Washington, depicted erroneously analyzed moisture fields. We issued a Base
warning for gusty surface winds up to 35 mph without thunderstorms, effective at 9
p.m. local time. This forecast gravely underestimated the gravity of the situation.
Shortly after 9 p.m., stations to our west and southwest began reporting lightning and
by 9:30 thunderstorms were in progress and, to our surprise, detectable only twenty
miles to the southwest of the Base. Even on our crotchety old AN-PQ-13 radar * the
leading thunderstorm cells looked vicious and were moving very fast. The Sergeant
began typing up a warning for thunderstorms accompanied by stronger gusts even
though we were too late to alert the Base and secure the aircraft. At 9:52 p.m. the
squall line moved across Will Rogers Airport 7 miles to our west southwest. To our
horror they reported a heavy thunderstorm with winds gusting to 92 miles per hour
and worst of all at the end of the message, "TORNADO SOUTH ON GROUND
MOVING NE!"We had it for certain! We could only pray that this storm would
change course and move southeast. There was no such miracle and at 10 p.m. the
large tornado, visible in a vivid background of continuous lightning, and
accompanied by crashing thunder began moving from the southwest to northeast
across the base. We watched it, not really believing, as it passed just east of the large
hangars and the operations building where we crouched in near panic. Suddenly the
glass in the control tower to our right succumbed to the pressure differential caused by
the vortex, and all the glass shattered. The control tower personnel were badly cut.
They had not abandoned the tower despite the 78 mile an hour winds around the outer
fringe of the tornado. Seconds later the Operation Building's large window blasted
outward into the parking area. Debris filled the air. Then, suddenly, the churning
funnel lifted and dissipated over the northeast edge of the Base.
* Originally intended and used as a bomb-aiming radar on B-29's in WW II, this radar
was extensively employed for storm detection by Air Weather Service in the Post-war
period. It had an ostensible range of 100 miles.
March 21, 1948
At 10:00 A.M. the next day, an investigative board of five General Officers flew into
the ravaged base from Washington D.C. and convened an hour later. Major Fawbush
(E. J. to me) and I waited our turn "on the grill" with considerable trepidation. I was
especially tense, having performed in such a abysmal manner the previous evening. It
really didn't seem fair that a bright young forecaster, native to an area where a mild
thunderstorm was considered a holiday event that caused people to run outside and
gesticulate skyward mouthing such phrases as "golly" and "wow", should be thrust
into an area subject to such miserable phenomena. The time came and we were
ushered into the room. We snapped to attention with E. J. advising the board, in a
garrulous voice, "Major Fawbush and Capt. Miller, reporting as directed." We were
put at ease (a most inappropriate phrase), and the interrogation began. The questions
were well put, concise and fair and we were both impressed. E. J. described the events
of the previous evening but did not mention the erroneous facsimile charts. We felt,
perhaps wrongly in retrospect, that this would result in a great political hassle of
dubious value to anyone. E. J. described the difficulty involved in forecasting
tornadoes and the resultant reluctance of the weather services to issue warnings to the
public. The board reached its decision early that afternoon. They decided that”due to
the nature of the storm it was not forecastable given the present state of the
art" and that "it was an act of God" - which it most certainly was. They
recommended that the meteorological community consider efforts to determine a
method of alerting the public to these storms and urged Base Commanders to
develop safety precautions to minimize personnel and property losses in violent
storms.
That afternoon the Commanding General of the Oklahoma City Air Material Area,
Fred S. Borum, directed the Air Weather Service to have the Tinker Base Weather
Station (under the command of Major Ernest J. Fawbush), investigate the feasibility of
forecasting tornado-producing thunderstorms. Major Fawbush had been interested for
some years in such storms and since I had become "most interested" overnight, I was
most fortunate in being selected to aid in the investigations.
March 22 - 24, 1948
In the three days of highly concentrated effort we analyzed not only the surface
and upper-air weather charts prior to the Tinker tornado, but for several other
past tornadic outbreaks. Certain similarities in the weather patterns preceding such
storms did appear and, in addition, supported theories advanced by other researchers
interested in the cause and behavior of tornadoes. Using our findings and
incorporating those of others - most notably, excellent work by USWB personnel such
as the late Mr. J. R. Lloyd, Meteorologist in charge at Kansas City, Missouri and an
extremely useful paper by A. K. Showalter and J. R. Fulks (also with the USWB) - we
listed several weather parameters considered sufficient to result in significant tornadic
outbreaks when all were present in a geographical area at the same time. The
problem faced by the forecaster was to consider the current surface and upper
air data, determine the existence of these parameters or the probability of their
development, and then project the parameters in space and time in order to issue
the "tornado threat area" with a reasonable degree of confidence and leadtime. The size of the threat area would cover 20-30,000 square miles. Such a detailed
forecast procedure was time and labor consuming and required intensive and
specialized analysis.
March 25, 1948
On the morning weather charts of the 25th of March 1948, just five days after the
Tinker storm, we noted a great similarity between the charts of the 20th and the
25th. After analyzing the surface and upper-air data, a prognostic chart was prepared
for 6:00 p.m. local time showing the expected position of the various critical
parameters. This chart resulted in the somewhat unsettling conclusion that central
Oklahoma would be in the primary tornado threat area by late afternoon and
early evening. General Borum was notified and shortly thereafter arrived at the
weather station.
He was very interested and most knowledgeable when it came to weather. He was
highly proficient in the operation of our local radar and loved to watch the scope
during thunderstorm outbreaks. He digested what we had told him and asked, "Are
you planning to issue a tornado forecast for Tinker?" There was a period of
uneasy quiet until E. J. spoke up.
"Well it certainly looks like the 20th, right Bob?"
Oh, great! I wanted to turn and ask my Sergeant friend the same question, but he
wasn't on shift.
I replied, "Yes, E. J., it certainly looks like it did on the 20th."
After hearing these helpful observations, the General asked what we believed the
critical time would be and received a useful answer this time -- 5 to 6 p.m. The
General then decided we should issue a forecast for heavy thunderstorms during
that period. He patiently explained that such a move would serve to alert the base and
set phase A of his brand new, and detailed, base warning system into effect. We were
more than delighted with this approach, knowing in our hearts that we were "off the
hook" since this would cover us. The chance of a second tornado hitting the same spot
within five days was less than 1 in 20,000,000. Far better we should take such odds
rather than actually issue a tornado forecast and be laughed out of Uncle Sam's Air
Force. We issued the General's heavy thunderstorm warning -- what else?
As the day progressed, reports we received over the weather teletype network,
confirmed our opinion that the weather pattern was indeed strikingly similar to that
which produced the tornado on the 20th. Events were moving more swiftly, however,
and any organized severe weather activity would occur during the afternoon. Stations
to our west and southwest began reporting building cumulus clouds shortly after noon
and by 1:30 p.m. Wichita Falls, Texas and Altus, Hobart, and Enid, Oklahoma were
reporting cumulonimbus. At 1:52 p.m. the first thunderstorm echoes appeared on the
radar scope 60 miles to our northwest and extended 100 miles to our southwest. By 2
p.m. they were beginning to increase in number and size and organizing into a squall
line. When notified of this development, General Borum headed for the weather
station at once. The General spent ten minutes scanning the radar scope and
commented on the rapid development and increasing intensity of the squall line. By
2:30 p.m. we determined the line was moving toward Tinker at 27 mph which would
place it over the base near 6 p.m. E. J. and I glanced rather apprehensively at each
other, sensing what was going to happen next. General Borum stood up, looked us in
the eye and asked the unsettling question, "Are you going to issue a tornado
forecast?" I knew E. J. would come up with a sensible, honest answer and he did.
"Well, Sir, it sure does look like the last one, doesn't it Bob?"
I tried to think of a brilliant answer and found myself saying, "Yes E. J., it is very
similar to last week."
The General was not particularly impressed with this intelligence: "You two sound
like a broken record. If you really believe this situation is very similar to the one last
week, it seems logical to issue a tornado forecast."
We both made abortive efforts at crawling out of such a horrendous decision. We
pointed out the infinitesimal possibility of a second tornado striking the same area
within twenty years or more, let alone in five days. "Besides," we said, "no one has
ever issued an operational tornado forecast."
"You are about to set a precedent", said General Fred S. Borum.
With a sinking feeling in the pits of our stomachs, E. J. composed the historic
message and I typed it up and passed it to Base Operations for dissemination.
The time was 2:50 p.m. The General left, asking to be kept informed of significant
developments. We discussed our suddenly impossible predicament. It seemed a
hopeless situation, one where we couldn't win and the General couldn't lose. Base
Personnel were carrying out his detailed Tornado Safety Plan, hangaring aircraft,
removing loose objects, diverting incoming air traffic and moving base
personnel, including the control tower personnel, to places of relative safety. I
could see it now, a sure "bust" and plenty of flack thereafter. I figured General Borum
wasn't about to say, "I made them do it". More likely it would be, "Major Fawbush
and Captain Miller thought it looked a great deal like the 20th - ask them." I wondered
how I would manage as a civilian, perhaps as an elevator operator. It seemed
improbable that anyone would employ, as a weather forecaster, an idiot who issued a
tornado forecast for a precise location.
The squall line was fully developed by half past three and continued to move steadily
toward Oklahoma City. There had been neither reports of tornadoes nor any reports of
hail and high winds, as yet. We were both very apprehensive and at this point would
settle gratefully for a loud thunderstorm with a brilliant lightning display and
hopefully a wind gust to 30 or 40 mph with perhaps some small hail. General W. O.
Senter, commander of the Air Weather Service would perhaps be more merciful if we
could just get a reasonably heavy thunderstorm. Shortly after 5 p.m. the squall line
passed through Will Rogers Municipal Airport, but this time they not only didn't
report a tornado, but infinitely worse, a light thunderstorm, wind gusts to 26
mph and pea size hail. That did it, I abandoned ship, leaving a grim Major
Fawbush to go down with the vessel.
I drove directly home. E. J. and I both lived in Midwest City, just across the highway
on the north side of the base. I related the events of the day to my wife, Beverly, who
was reasonably sympathetic, and then sat down to aggravate my depression
systematically. A little after six o'clock it began to thunder rather quietly and rain
began. There was very little wind. It became quite dark and over the base, portions of
the clouds seemed to be boiling while low cloud fragments darted hither and yon
beneath the base of the thunderstorm. My view was quickly obscured by heavy rain
and I stopped observing the storm. During the evening the radio broadcast we were
listening to was interrupted for an urgent news bulletin. I was in another part of the
house but caught the words destructive tornado and Tinker Field. "Good grief", I
thought, "they're still talking about last week's tornado -- but why break into the
news." I tried to call the weather station but the lines were dead. I felt a strange
unbelieving excitement rising, told my wife I was going to the station and drove away.
The base was a shambles. Poles and power lines were down and debris was strewn
everywhere. Emergency crews were busy trying to restore power, clear the streets
and, in particular, to restore the main runway to operational status. I reached the
station to find a jubilant Major Fawbush who described the course of events after I
had given up hope. At six o'clock thunder began at the base as the squall line moved
in from the southwest. E. J. and my friend, the Sergeant, were outside, observing the
motion of the clouds. As the line approached the southwest corner of the field, two
thunderstorms seemed to join and quickly took on a greenish black hue. They
could observe a slow counterclockwise cloud rotation around the point at which
the storms merged. Suddenly a large cone shaped cloud bulged down rotating
counterclockwise at great speed. At the same time they saw a wing from one of the
moth-balled World War II B-29's float lazily upward toward the visible part of the
funnel. A second or two later the wing disintegrated, the funnel shot to the
ground and the second large tornado in five days began its devastating journey
across the base very close to the track of its predecessor.
It was all over in 3 or 4 minutes. It seemed much longer. The swirling funnel left
$6 million dollars in damage, $4 million less than the first storm and
significantly, there were no personal injuries. General Borum's Tornado Disaster
Plan had been just as successful as the first operational tornado forecast. We
became instant heroes, and in my case, the rest of my life would be intimately
associated with tornadoes and severe thunderstorms. General Borum graciously
refrained from mentioning the story behind the sensational forecast and he convinced
General Senter that we should be allowed to concentrate on further development of
our forecast system. Ernest K. Gann's title, "Fate is the Hunter," * (* Fate is The
Hunter, Ernest K. Gann, Doubleday.) strikes me as most appropriate. The complexity
and evolution of the pattern that instigated the sequence of events I have described
boggles the mind. This first tornado forecast triggered a chain of events which led
to the present day Severe Storms Forecast System and a vast national research
program investigating these killer storms. Well, it did look a lot like March 20th.
Even the General thought so.
The Fujita Scale is used to rate the intensity of a tornado by examining the damage caused by
the tornado after it has passed over a man-made structure.
The "Percentage of All Tornadoes 19501994" pie chart reveals that the vast
majority of tornadoes are either weak or do
damage that can only be attributed to a weak
tornado. Only a small percentage of
tornadoes can be correctly classed as violent.
Such a chart became possible only after the
acceptance of the Fujita Scale as the official
classification system for tornado damage. It
is quite possible that an even higher
percentage of all tornadoes are weak. Each
year the National Weather Service documents about 1000 tornado touchdowns in the United
States. There is evidence that 1000 or more additional weak tornadoes may occur each year and
go completely undocumented.
The "Percentage of Tornado-Related
Deaths 1950-1994" pie chart shows that
while violent tornadoes are few in number,
they cause a very high percentage of tornadorelated deaths. The Tornado Project has
analyzed data prior to 1950, and found that
the percentage of deaths from violent
tornadoes was even greater in the past. This
is because the death tolls prior to the
introduction of the forecasting/awareness
programs were enormous: 695 dead
(Missouri-Illinois-Indiana, March 18, 1925);
317 dead(Natchez, Mississippi, May 7, 1840);.255 dead(St. Louis, Missouri and East St. Louis,
Illinois, May 27, 1896); 216 dead(Tupelo, Mississippi, April 5, 1936); 203 dead(Gainesville,
GA, April 6, 1936). In more recent times, no single tornado has killed more than 50 people since
1971.
The Fujita Scale (also known as the Fujita-Pearson Scale) may not be a perfect system for
linking damage to wind speed, but it had distinct advantages over what had gone on before its
inception. And it was simple enough to use in daily practice without involving much additional
expenditure of time or money. From a practical point of view, it is doubtful that any other system
would have found its way into widespread accepted use, even to this day. The entire premise of
estimating wind speeds from damage to non-engineered structures is very subjective and is
difficult to defend from various meteorological perspectives. Nothing less than the combined
influence and prestige of the late Professor Fujita and Allen Pearson, director of NSSFC
(National Severe Storm Forecast Center) in 1971 could have brought this much needed system
into widespread use. The FPP scale rates the intensity of the tornado, and measured both the path
length and the path width. The Fujita part of the scale is as follows:
The Fujita Scale
F-Scale
Number
F0
Intensity
Phrase
Gale tornado
Wind
Speed
Type of Damage Done
Some damage to chimneys;
40-72 breaks branches off trees; pushes
mph
over shallow-rooted trees;
damages sign boards.
73112
mph
The lower limit is the beginning
of hurricane wind speed; peels
surface off roofs; mobile homes
pushed off foundations or
overturned; moving autos
pushed off the roads; attached
garages may be destroyed.
F2
Significant
tornado
113157
mph
Considerable damage. Roofs torn
off frame houses; mobile homes
demolished; boxcars pushed
over; large trees snapped or
uprooted; light object missiles
generated.
F3
Severe
tornado
158206
mph
Roof and some walls torn off well
constructed houses; trains
overturned; most trees in forest
uprooted
F4
Devastating
tornado
207260
mph
Well-constructed houses leveled;
structures with weak foundations
blown off some distance; cars
F1
Moderate
tornado
thrown and large missiles
generated.
F5
F6
Incredible
tornado
Inconceivable
tornado
261318
mph
Strong frame houses lifted off
foundations and carried
considerable distances to
disintegrate; automobile sized
missiles fly through the air in
excess of 100 meters; trees
debarked; steel re-enforced
concrete structures badly
damaged.
319379
mph
These winds are very unlikely.
The small area of damage they
might produce would probably
not be recognizable along with
the mess produced by F4 and F5
wind that would surround the F6
winds. Missiles, such as cars and
refrigerators would do serious
secondary damage that could not
be directly identified as F6
damage. If this level is ever
achieved, evidence for it might
only be found in some manner of
ground swirl pattern, for it may
never be identifiable through
engineering studies
A key point to remember is this: the size of a tornado is not necessarily an indication of its
intensity. Large tornadoes can be weak, and small tornadoes can be violent. A good example of
a relatively "small" tornado would be the Pampa, Texas tornado of 1995, which can be seen in
Tornado Video Classics III. Eyewitnesses to this tornado claim to have seen as many as 6
vehicles in the air at the same time when it passed over a parking lot. Another consideration is
the stage in the life cycle of the tornado. A "small" tornado may have been larger, and is at the
"shrinking" stage of its life cycle, like the Tracy, Minnesota tornado. Large tornadoes can also be
strong and small tornadoes can be weak. The Fujita Scale is based on damage, not the
appearance of the funnel. Storm spotters, storm chasers and other weather observers often try to
estimate the intensity of a tornado when they are in the field, basing their judgment on the
rotational speed and amount of debris being generated as well as the width. However, the official
estimate is made after the tornado has passed. Personnel from the National Weather Service
office that issued the warning survey the site to determine the F-Scale rating. Sometimes they
call in experts from out of the area. Aerial surveys are occasionally done after violent tornadoes
to determine the exact damage track. Insurance companies may also call in wind engineers to do
their own evaluations, but the official rating is set by the NWS. A few of the things they all look
for are:




attachment of the walls and floor to the foundation of the building
attachment of the roof to the rafters and walls
whether or not there are steel reinforcing rods in concrete or cinder block walls
whether there is mortar between the cinder blocks
After the NWS office does the survey, the official rating is recorded, and eventually posted at
the SPC site. If it is a killer tornado we also post the rating on our site with the description of the
event, and on our "all tornadoes" page. The NWS office may also write up a more extensive
report, which may or may not be posted on the web. A good example of such a report would be
the one done on the Florida tornadoes of March, 1998.
The Fujita Scale is very subjective, and varies according to how experienced the surveyor is.
We have many readers who have tried to do their own "surveys" of tornado damage when storms
have occurred in their area. However, the less experienced the surveyor is, the more likely he/she
is to be awed by the damage, and the more likely they are to give it a high rating. Brian Smith of
the Omaha, Nebraska area NWS office, a former student of Dr. Fujita and an expert frequently
brought in to do site surveys, tells of hearing about a tee-shirt with the words "F-3 My Foot"
printed on it.
Media hype and inexperience with tornado damage also plays a big part in exaggerated F-Scale
claims seen on television or in the paper. A reporter may see a collapsed concrete block home
and be very impressed, never noticing that there was no mortar between the blocks. They may be
aghast to see a park whose trees have been leveled, but not know that the species had very
shallow roots, planted in soil that was soft and soggy from torrential rains, and thus easily
toppled. They may see a roof that had been blown a quarter of a mile from its house, and not
know that the roof was attached to the house with only a few nails, and when lofted into the air,
acted as a "sail." They may see a light post that is bent at a 30 degree angle and think that it must
have taken a 600 mph wind to do that, not knowing that a van had been blown into the pole,
bending it, then been towed off to help clear the streets. For some of the media, the exaggerations
make for a better story than the actual facts. Fortunately, they often make up for this by printing
helpful stories about aid available and inspirational human interest stories.
As if doing a site survey of a track is not difficult enough, tornadic storms may also be
accompanied by complex combinations of strong downbursts and other straight line winds.
Separating tornado damage from
other wind damage makes for a
daunting, difficult task for even the
most experienced surveyor.
The Seymour, Texas, tornado of
April 10, 1979 is a prime example of
a tornado that is destined to be misjudged on the Fujita Scale. This spectacular funnel was
probably capable of F4 damage, had it passed through a town. It produced only telephone pole
and tree damage, and thus could be rated no higher than F2 damage. The Seymour tornado was
in the same family as the devastating Wichita Falls, Texas tornado, which remains as of this
writing, the most damaging in US history. Video of this tornado is used in the Fujita Scale
segment of Tornado Video Classics II
Professor Fujita continued his work until his death at the age of 78. Mr. Pearson is semi-retired,
and is very active on the web.
We intend to supply the US data in three steps:
1. The first step is to put up the information for all US tornadoes from 1950 to
1995.
2. The second step is to put up the eastern US information, back to 1700.
3. The third step to put up information for all US states back to 1800, or as far as
we can.
All tornadoes regardless of intensity will be included.
Some of this data is already available in zipped form at the Storm Prediction Center
site, but we intend to extend the data base as well and provide it in an easy to access
form. It will complement their data, not attempt to eliminate the need for it or replace
it.
Dallas County Tornadoes
MAR
APR
APR
APR
JUN
AUG
OCT
MAY
MAY
APR
MAY
MAY
SEP
MAY
MAR
MAY
MAY
MAY
02,
02,
03,
20,
12,
12,
04,
05,
05,
11,
27,
29,
05,
23,
26,
13,
25,
08,
1952
1957
1957
1957
1957
1958
1959
1960
1960
1961
1963
1963
1963
1966
1967
1968
1968
1969
002
028
040
051
127
062
079
024
025
030
023
025
069
035
012
043
055
047
2200
1630
1050
0020
0810
1435
0600
2200
2237
1655
1900
1800
1331
1430
0500
0242
2100
1524
0
10
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
200
0
0
0
0
0
0
0
3
0
0
0
0
0
0
1
0
F0
F3
F0
F1
F3
F2
F3
F0
F0
F2
F0
F0
F1
F2
F0
F1
F0
F0
113
113
113
113 139
113
113
113 397
113
113
113
113
113
113
113
113
113
113
113
OCT
APR
FEB
OCT
DEC
DEC
DEC
DEC
DEC
NOV
NOV
MAY
APR
JUN
JUN
JLY
MAR
MAY
JLY
APR
MAY
MAY
MAY
MAY
MAY
OCT
MAR
APR
MAY
MAR
DEC
DEC
MAY
MAR
JAN
OCT
MAY
APR
APR
APR
APR
OCT
OCT
OCT
OCT
MAR
APR
APR
12,
25,
18,
19,
14,
14,
14,
14,
14,
12,
12,
01,
11,
12,
08,
25,
26,
26,
04,
20,
03,
03,
03,
03,
08,
13,
14,
16,
11,
23,
13,
13,
13,
16,
19,
07,
09,
25,
25,
25,
29,
21,
21,
21,
21,
25,
19,
19,
1969
1970
1971
1971
1971
1971
1971
1971
1971
1972
1972
1973
1974
1974
1975
1975
1976
1976
1976
1977
1979
1979
1979
1979
1981
1981
1982
1982
1982
1984
1984
1984
1985
1987
1990
1992
1993
1994
1994
1994
1994
1994
1994
1994
1994
1995
1995
1995
119
020
005
164
176
179
181
184
186
139
140
070
014
067
082
105
006
114
147
034
068
069
072
074
041
164
005
020
060
017
091
091
050
003
001
162
042
013
014
015
050
174
175
176
179
019
031
050
0650
0500
1720
2037
1730
1800
1800
1815
1830
2130
2150
1345
0510
0515
1826
1110
1430
1625
2000
0055
1030
1048
1305
1325
2020
1340
0725
1650
2015
1645
0945
0951
1042
1340
1130
1612
1230
1950
2000
2030
0115
1456
1550
1612
1700
1745
1420
2002
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
0
3
0
0
0
0
0
0
0
0
2
12
0
2
1
0
1
4
4
0
0
0
0
0
0
0
0
1
0
0
0
0
5
0
0
0
0
0
1
0
0
28
16
0
1
0
1
0
7
48
0
0
0
0
0
0
0
8
F3
F2
F1
F1
F1
F1
F1
F2
F1
F1
F1
F1
F2
F1
F0
F0
F1
F3
F1
F2
F1
F1
F2
F0
F2
F1
F1
F0
F1
F1
F3
F3
F2
F0
F2
F0
F1
F0
F2
F4
F0
F0
F0
F0
F0
F0
F0
F1
STORM EVENTS LINK: http://www.ncdc.noaa.gov/stormevents/
113
113
113
113
113 439
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113
113