Tornadoes
What is a tornado?
A tornado is a violently rotating
column of air extending from a
thunderstorm to the ground.
A thunderstorm is, in general, a local
storm, invariably produced by a
cumulonimbus cloud and always
accompanied by lightning and thunder,
usually with strong gusts of wind, heavy
rain, and sometimes with hail.
The typical thunderstorm is 15 miles in
diameter lasts an average of 30 minutes.
Of the estimated 100,000 thunderstorms
that occur each year in the United
States, about 10 percent are classified
as severe.
Is a tornado a
cyclone?
Yes, a tornado is a cyclone. But a
hurricane is a cyclone too. A cyclone
is a general term referring to an
area of closed circulation. While a
tornado is a type of cyclone, so too
is a hurricane, and even the big "L"
you see on a weather map. The "L"
on the weather map stands for low
pressure, but it is on a synoptic
scale (a large scale measuring
hundreds of miles or more), while a
tornado is on a micro-scale or
storm-scale.
Tornadoes are found most
frequently in the US
In an average year,
1,200 tornadoes cause
70 fatalities and 1,500
injuries nationwide.
"Tornado Alley," or the
states at the highest risk of
getting a tornado, include
Arkansas, Iowa, Kansas,
Louisiana, Minnesota,
Nebraska, North Dakota,
Ohio, Oklahoma, South
Dakota, and Texas.
How does a tornado form?
Most tornadoes form from
thunderstorms. You need warm, moist
air from the Gulf of Mexico and cool,
dry air from Canada. When these two
air masses meet, they create
instability in the atmosphere.
North America is a relatively large
continent that extends from the
tropical south into arctic areas, and
has no major east-west mountain
range to block air flow between these
two areas. This unique topography
allows for many collisons of warm and
cold air; creating the conditions
necessary to breed strong, long-lived
storms which occur many times a
year.
Tornado
Alley
How does a tornado form?
Under tornado-favorable condition,
a 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.
Step 1: Spinning in the
lower atmosphere
How does a tornado form?
Rising air within the updraft tilts
the rotating air from horizontal
to vertical.
Step 2: Lifted and tilted from
horizontal to vertical
How does a tornado form?
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.
Step 3: Extending and Forming
Tornadoes Take Many Shapes and Sizes
Weak Tornadoes
Strong Tornadoes
Violent Tornadoes
88% of all tornadoes
Less than 5% of tornado deaths
Lifetime 1 - 10+ minutes
Winds less than 110 mph
11% of all tornadoes
Nearly 30% of all tornado deaths
May last 20 minutes or longer
Winds 110-205 mph
Less than 1% of all
tornadoes
70% of all tornado deaths
Lifetime can exceed 1 hour
Winds greater than 205 mph
Fujita Scale of Tornado Intensity
SCALE WIND SPEED
POSSIBLE DAMAGE
F0
40-72 mph
Light damage: Branches broken off trees; minor roof damage
F1
73-112 mph
Moderate damage: Trees snapped; mobile home pushed off
foundations;roofs damaged
F2
113-157 mph
Considerable damage: Mobile homes demolished; trees
uprooted; strong built homes unroofed
F3
158-206 mph
Severe damage: Trains overturned; cars lifted off the
ground; strong built homes have outside walls blown away
F4
207-260 mph
Devastating damage: Houses leveled leaving piles of
debris; cars thrown 300 yards or more in the air
F5
261-318 mph
Incredible damage: Strongly built homes completely
blown away; automobile-sized missiles generated
Where and when tornadoes occur?
Tornadoes can occur at any time of the year
and any time of the day.
Tornadoes have occurred in every state, but
they are most frequent east of the Rocky
Mountains during the spring and summer
months.
In the southern states, peak tornado
occurrence
is March through May, while peak months in
the northern states are during the late spring
and summer.
Tornadoes are most likely to occur between
3 and 9 p.m. but can happen at any time.
Deport, Texas
Hoxie, Kansas
Northeast, Nebraska
Tornado in Salt Lake City
Salt Lake City Tornado,
Aug. 11, 1999
Orange fireball is a power substation exploding.
On August 11, 1999, an F2 tornado touched down in the
metropolitan area of Salt Lake City. The tornado lasted ten
minutes and killed one person, injured more than 80
people, and caused more than $170 million in damages. It
was the most destructive tornado in Utah's history.
Tornado Statistics for
Utah January 1950 to
Present
Total Tornadoes: 124
Number of Injuries:
Number of Deaths:
Number of Tornadoes
by Month
January
1
February
1
March
4
April
7
May
29
June
18
July
15
August
24
September
21
October
0
November
2
December
2
.
2 people on July 8, 1989
1 male on August 14, 1968
1 female on April 19, 1970
1 male on April 23, 1990
2 people on June 2, 1993
1 female on May 29, 1996
5 people (or more) on August 20,
1998
80 people (or more) on August 11,
1999
1 female on September 3, 1999
1 male on August 11,
1999
(Note: 1 young female
was killed on July 6,
1884.)
What is a waterspout?
A waterspout is just a weak
tornado that forms over water.
They are most common along the
Gulf Coast. Waterspouts can
sometimes move inland,
becoming tornadoes causing
damage and injuries.
What is a gustnado?
A gustnado is a short-lived,
relatively weak whirlwind that
forms along a gust front. A
gust front is the surge of very
gusty winds at the leading
edge of a thunderstorm's
outflow of air.
Gustnadoes are not
tornadoes. They do not
connect with any cloud-base
rotation. But because
gustnadoes often have a
spinning dust cloud at ground
level, they are sometimes
wrongly reported as
tornadoes.
Gustnadoes can do minor
damage.
A gustnado in southeastern Wisconsin on 4
October 2002.
Weather Radar Watches the Sky
Storm relative motion images from the Evansville Doppler
Radar (VWX) at 1:58 a.m., which was near the time the
tornado ripped through the Eastbrook Mobile Home Park.
Note the strong rotational couplet.
Damage by the CRITTENDENWEBSTER COUNTY KENTUCKY F-3
TORNADO, November 6 2005
Tornado watch and warning
TORNADO WATCH Tornadoes are possible
in your area. Stay tuned
to the radio or television
news.
TORNADO WARNING A tornado is either on the
ground or has been
detected by Doppler
radar. Seek shelter
immediately!
Red: Tornado Warning
Purple: Flash Flood Warning
To see if there are any active warnings in your
area, go to:
http://www.weather.gov/view/largemap.php
Tornado Facts
1. Tornadoes may appear nearly transparent until dust and debris are picked
up or a cloud forms within the funnel.
2. The average tornado moves from southwest to northeast, but tornadoes
have been known to move in any direction.
3. The average forward speed is 30 mph but may vary from nearly stationary
to 70 mph.
4. The strongest tornadoes have rotating winds of more than 250 mph.
5. Tornadoes can accompany tropical storms and hurricanes as they move
onto land.
Tornado Safety Tips
BEFORE A TORNADO: Have a disaster plan. Make sure everyone knows where
to go in case a tornado threatens. Make sure you know which county or parish
you live in. Prepare a disaster supplies kit for your home and car. Include a first
aid kit, canned food and a can opener, bottled water, battery-operated radio,
flashlight, protective clothing and written instructions on how to turn off electricity,
gas, and water.
DURING A TORNADO: Go to a basement. If you do not have a basement, go to
an interior room without windows on the lowest floor such as a bathroom or closet.
If you can, get under a sturdy piece of furniture, like a table. If you live in a mobile
home get out. They offer little protection against tornadoes. Get out of
automobiles. Do not try to outrun a tornado in your car, leave it immediately. If
you’re outside, go to a ditch or low lying area and lie flat in it. Stay away from
fallen power lines and stay out of damaged areas.
IF YOU’RE AT SCHOOL DURING A TORNADO: Every school should have a
disaster plan and have frequent drills. Basements offer the best protection.
Schools without basements should use interior rooms and hallways on the lowest
floor away from windows. Crouch down on your knees and protect your head with
your arms.
AFTER A TORNADO: Stay indoors until it is safe to come out. Check for injured
or trapped people, without putting yourself in danger. Watch out for downed power
lines. Use a flashlight to inspect your home.
Tornado Videos