Tornadoes

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Tornadoes
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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.
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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.
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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.
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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
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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
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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
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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
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Tornadoes Take Many Shapes and Sizes
Violent Tornadoes Less than 1 of all
tornadoes 70 of all tornado deaths Lifetime can
exceed 1 hour Winds greater than 205 mph
Strong Tornadoes 11 of all tornadoes Nearly 30
of all tornado deaths May last 20 minutes or
longer Winds 110-205 mph
Weak Tornadoes 88 of all tornadoes Less than 5
of tornado deaths Lifetime 1 - 10 minutes Winds
less than 110 mph
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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
foundationsroofs 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
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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
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Tornado in Salt Lake City
Salt Lake City Tornado, Aug. 11, 1999
Orange fireball is a power sub-station 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.
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Tornado Statistics for Utah January 1950 to
Present
Number of Injuries 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
Total Tornadoes 124 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 .
Number of Deaths 1 male on August 11,
1999 (Note 1 young female was killed on July 6,
1884.)
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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.
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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.
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Weather Radar Watches the Sky
Storm relative motion images from the Evansville
Doppler Radar (VWX) at 158 a.m., which was near
the time the tornado ripped through the Eastbrook
Mobile Home Park. Note the strong rotational
couplet.
Damage by the CRITTENDEN-WEBSTER COUNTY KENTUCKY
F-3 TORNADO, November 6 2005
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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/l
argemap.php
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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.
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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 youre 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 YOURE 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.
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Tornado Videos