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Severe Weather Awareness Week » Tornadoes
Southeast Texas Severe Weather Awareness Week
February 24 - March 1, 2008 |
TORNADOES
What causes tornadoes?
Tornadoes most commonly form from large-scale storm systems that traverse
the U.S. from west to east. Typically, severe thunderstorms will develop in the
warm, moist airmass ahead of the storm system, and can produce tornadoes.
Tornadoes can result from isolated thunderstorms or as part of a large squall
line that forms along a cold front. Severe thunderstorms and tornadoes need an
unstable (warm, humid) airmass, cold air at mid-levels of the atmosphere, and
strong wind shear (turning and strengthening of winds with height in the atmosphere)
to develop. In a thunderstorm, the tornado begins as a circulation several thousand
feet above the ground, and slowly descends to the ground.
Organized tropical systems like tropical storms and hurricanes can also produce
tornadoes, but usually smaller and shorter-lived than those spawned by mid-latitude
systems.
How do tornadoes impact Southeast Texas?
Texas averages 137 tornadoes each year, the highest number of any state in the
U.S. Tornadoes are most common during the spring and summer months nationwide, but
due to our proximity to the Gulf of Mexico as a moisture source, tornadoes can occur
in southeast Texas any time of year. In fact, some of the worst tornado outbreaks
on record in southeast Texas have actually occurred in the late fall and winter
months. Strong to violent tornadoes (those F2 or larger) are fairly uncommon in
southeast Texas, but they can occur. Tornadoes in southeast Texas are usually
isolated incidences, but occasionally can occur in "outbreaks" of several in one day.
What is a waterspout?
Waterspouts are weak tornadoes that form over water. Along the upper Texas coast
they are most common during the morning hours of the summer months, and do not require
a thunderstorm to be present to form. Usually, waterspouts are short-lived, do little
if any damage, and have winds well under 100 mph. On rare occasions, they can move
inland as tornadoes and cause damage.
How are tornadoes rated?
Weak tornadoes are generally those classified as EF-0 or EF-1 and comprise 69% of all
tornadoes nationally and 93% of all tornadoes locally. In southeast Texas...these
tornadoes typically last only a few minutes and produce winds less than 100 mph.
Usually, they will cause only spotty minor damage, such as downing trees or power lines.
Tornadoes in the EF-0 or EF-1 category contribute to less than 5% of tornado deaths annually.
Strong tornadoes are those classified as EF-2 or EF-3, with winds of 111 to 165 mph.
They comprise 29% of all tornadoes and account for nearly 30% of all tornado deaths across
the entire U.S.. They may last twenty minutes or longer. Tornadoes of this magnitude are
uncommon in southeast Texas, accounting for only 7% of all tornadoes that have affected
the area.
Violent tornadoes, those classified as EF-4 or EF-5, account for only 2% of all tornadoes
nationwide. These tornadoes account for 70% of all tornado deaths nationally, and their
lifetime can exceed one hour. Violent tornadoes have occurred in southeast Texas, but they
are extremely rare. These tornadoes only account for less than 1% of all tornadoes
that have ever struck southeast Texas.
Tornado rating has nothing to do with the size of the tornado. Each tornado is rated
after it touches down, based on the damage that it has done.
| Enhanced F Scale for Tornado Damage |
| No. |
Wind Speed (3 sec gust in mph) |
Damage |
| EF-0 |
65-85 |
Light |
| EF-1 |
86-110 |
Moderate |
| EF-2 |
111-135 |
Considerable |
| EF-3 |
136-165 |
Severe |
| EF-4 |
166-200 |
Devastating |
| EF-5 |
Over 200 |
Incredible |
What are some tornadoes and tornado outbreaks that have impacted Southeast Texas?
- March 30, 2002
- An F3 tornado struck the La Porte area on this evening. The tornado began its path
three miles south of La Porte and then moved northeast and partially demolished a mini
mart and caused major roof damage to an apartment complex. The path of this tornado
was 3/4 of a mil long.
- October 11, 2001
- An F2 tornado developed out of a thunderstorm that initially developed around Hobby
Airport just before 7:00 am. The storm moved to the east-northeast and continued to
strengthen. At around 7:05 am, the tornado touched down near the intersection of South
Shaver and Edgebrook Drives. The tornado traveled about 3.5 miles to the northeast
through Pasadena. The lifetime of the tornado was about 15 minutes...but the cost of
the damage was estimated to be somewhere between 3.5 and 4 million dollars. There were
no fatalities or injuries with this storm.
- July 12, 1999
A waterspout moved inland from Galveston Bay and struck the northern part of Texas
City as an F1 tornado. Severe damage occurred at an apartment complex.
- January 1, 1999
- Here's proof that tornadoes can occur any time of year in southeast Texas. On New
Year's Day 1999, nine tornadoes touched down over southeast Texas in association with
a strong storm system that was affecting the area. Two of the tornadoes were rated as
F2. One of the tornadoes tracked 5 miles to the south and east of Trinity...impacting
several subdivisions. The other F2 impacted an area in Liberty County 10 miles east
of Devers. Eight injuries were reported during this outbreak.
- February 16, 1998
- An F1 tornado struck First Colony Mall in Sugarland resulting in $3.7 million in
damage.
- October 23, 1997
- An unseasonably strong storm system spawned 11 tornadoes around southeast Texas.
Two F2 tornadoes were reported. One tornado tracked 12 miles from Lake Houston through
western Liberty County. Another tornado tracked 25 miles through Montgomery and Liberty
Counties, resulting in major damage to several homes and mobile homes. An F1 tornado
struck Sugarland damaging 109 homes. Total damage for the day was near $2.0 million.
- May 18, 1995
- A single storm produced 4 tornadoes in Liberty County. An F1 tornado struck Liberty,
injuring 12 and producing nearly $1 million in damage.
- April 15, 1994
- An F2 tornado hit Lake Houston and Indian Shores Estates resulting in 1 fatality and
20 injuries.
- November 16, 1993
- An outbreak of nine tornadoes occurred in the Houston area. An F1 tornado hit
downtown Houston, damaging an apartment complex and 30 automobiles, and resulting in 26
injuries.
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The November 1992 Outbreak
Perhaps the worst tornado outbreak on record in Southeast Texas occurred on November
21, 1992. Over a dozen tornadoes resulted from a powerful storm system moving across
the area. Most of the tornadoes occurred during a 2 hour period during the early afternoon
that day. Widespread damage occurred in the Houston area that day, with hundreds of
homes and businesses affected. A total of 34 injuries and over $12 million in damage
resulted from this outbreak. Amazingly, there were no fatalities.
An F4 tornado struck Channelview, tracking on the ground 20 miles into Liberty County.
At one point, the tornado widened to over a mile in diameter! This tornado resulted in
15 injuries, 200 homes destroyed, and 1000 homes damaged.
An F3 tornado was reported which tracked from Luce Bayou in northeastern Harris County
into Liberty County for a total of 28 miles. Two F2 tornadoes occurred in Harris County.
One tornado tracked right through the middle of Houston, traveling from Hermann Park
northward to near Intercontinental Airport damaging 600 buildings and injuring 6 people.
Another tornado struck the Kelliwood subdivision in Katy causing significant home damage
and injuring six. It then went on to hit the West Side Airport, tracking a total of 21
miles and damaging a dozen aircraft.
National Weather Service Tornado Products:
- TORNADO WATCH
Issued by the Storm Prediction Center in Norman, Oklahoma. Usually covers a fairly large
area (such as all or a portion of southeast Texas) and runs from 6 to 8 hours. A TORNADO
WATCH is usually issued a few hours in advance of severe weather, and means conditions
are favorable for severe thunderstorm development.
- TORNADO WARNING
Issued by your local National Weather Service office. Typically runs for a short time span,
usually 30 minutes to 1 hour and covers a relatively small area of one to a few counties.
Means a tornado has been sighted or a strong circulation has been detected by radar. If a
TORNADO WARNING is issued for your area, seek shelter immediately!!
Remember, tornadoes can occur even if a TORNADO
WATCH or a TORNADO WARNING are not in effect!!
What can you do ahead of time to prepare your home or business for a tornado threat?
- Develop a plan for your family or coworkers at your place of residence or business.
- Do frequent tornado drills.
- Know the county where you live. All National Weather Service warnings are issued by
county.
- Purchase a NOAA Weather Radio with a warning alarm tone and battery back-up. It will
automatically be activated when a warning is issued.
What do you do when a tornado is approaching or a TORNADO WARNING is issued?
- In a home or business, go to the safest place, usually on the lowest floor of the
building in a central room away from windows. Get under a sturdy piece of furniture.
- Stay away from windows.
- Get out of automobiles immediately! They will become flying debris in a tornado. Do
not try to outrun a tornado in your car.
- If caught outside, lie flat in a nearby ditch or depression.
- Abandon mobile homes. Even if tied down, they will offer no protection in a tornado.
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- Remain alert for signs of an approaching tornado.
- Be aware of rapidly darkening skies.
- Listen for approaching strong winds or the sound of a freight train.
- Look for rotation in clouds or a "wall cloud", a distinct lowering from the
back of a thunderstorm. In southeast Texas, hazy skies and tall trees make sighting
tornadoes difficult. Also, tornadoes are often obscured by rain or can occur at night.
- Remember, NEVER try to outrun a tornado in your car.
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What should a school do to prepare for a tornado?
1. Develop a severe weather action plan and conduct frequent drills. Children should
kneel on the floor, putting their head on the ground and covering their neck with their
hands. The neck and lower head are the most vulnerable parts of the body to flying debris.
2. Each school should be inspected and shelter areas designated by a registered engineer
or architect. Schools without basements should use interior rooms and hallways on the
lowest floor and away from windows.
3. Have a compressed air horn or megaphone to activate the alarm in case of power failure.
4. Make special provisions for disabled students or those in trailers.
5. Have someone on hand to turn off the gas or electricity if the school is damaged.
6. Prepare to keep children at school beyond regular hours if threatening weather is expected.
Children are safer in school than traveling on the roadways during severe weather.
Students should NOT be sent home early if severe weather is approaching.
7. Large, high rooms are dangerous when a tornado is approaching. Gymnasiums, cafeterias,
and auditoriums offer no protection in a tornado. Other large facilities can take similar
measures for tornado preparedness.
Tornado Statistics for Southeast Texas (1992-2007 graphs)
 Tornado Events (by month)- Tornado Events (by time)
- Tornado Intensity Statistics
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weather.gov 
National Weather Service Forecast Office
