saeedahmed.com

Saeed Ahmed - Staff
Monday, April 2, 2001

It was shortly before dawn on Valentine's Day last year when Caitlin Williams was awakened by a shrill noise that sounded like a freight train hurtling closer and closer.

Williams was visiting her grandmother in Camilla when four tornadoes ripped through the tiny Mitchell County town 200 miles south of Atlanta.

The twisters were the deadliest to hit Georgia in half a century. The violent whirling winds, which looked like huge black funnels, blew out roofs and walls.

Cars and livestock were picked up and tossed hundreds of feet.

Twenty-two people died and more than 250 were hurt.

The town suffered millions of dollars in damage.

"When it was over, it looked like someone had dropped an atomic bomb in our back yard," recalls Williams, who was 13 at the time.

The twisters that hit Camilla were unusual because winter tornadoes in Georgia are rare.

According to the National Weather Service, the peak months for the killer storms in Georgia are March, April and May.

The recipe for a tornado calls for a big thunderstorm, winds blowing from opposite directions and a strong "updraft" --- a lifting force that makes air rise.

And it all starts with a sandwich.

3-layer sandwich

In effect, three layers form a sandwich: warm air on the Earth's surface, a layer of warmer air in the middle and cold and dry air above.

The interaction of cold and warm air is the first step in forming a tornado.

During spring and summer in the United States, cold, dry winds moving south from the Rocky Mountains pile on top of warm, wet winds from the Gulf of Mexico.

In Georgia, warm winds also come from the southern part of the Atlantic Ocean.

Warm air is lightest and tends to rise, but cold air from the Rockies can block it.

Meanwhile, the sun heats the ground and warms more air, which keeps trying to rise.

As the surface air keeps heating, it builds up an enormous amount of energy --- much like boiling water in a pot with a heavy lid.

Then, when an advancing mass of cold air moves into the area, it displaces the warm air, bulldozing it upward.

The warm air punches through the layer that's holding it down in a process called an "updraft."

The updraft creates low air pressure near the ground, causing air from miles around to rush in.

As the air is sucked into the updraft, the moisture in it cools and condenses to form funnel-shaped clouds.

These clouds are known as "supercells," and they shower the ground with heavy rain and baseball-size hail.

This is why a burst of rain or hail often hits just before a tornado.

As the updraft continues to climb, it encounters winds of various speeds coming from various directions.

This is known as "wind shear" and it forces the rising air to rotate --- like water spiraling down a bathtub drain. This rotating column of air is a "mesocyclone."

No one knows for sure how a tornado develops out of this humid column of rotating air. In fact, most mesocyclones don't spawn tornadoes.

Occasionally, though, something happens to shape all that rotating and rising air into a more compact column --- a tornado --- that narrows and spins faster and faster down to the ground.

U.S. hit most: 800 times a year

The United States is home of the most tornadoes in the world. In an average year, 800 are reported nationwide.

The worst tornado outbreak in U.S. history occurred April 3-4, 1974, when 148 twisters touched down in 13 states, including Georgia.

In Georgia, there are an average of six tornado days per year. During "tornado season," tornadoes are most likely to hit from mid-afternoon through early evening.

Experts still debate whether the number of tornadoes that strike Georgia during this period is proof that the state has a "Tornado Alley." That's the name given to an area --- such as the Midwest --- that's especially prone to being hit by twisters.

Rating the trouble from F-O to F-6

Forecasters and researchers use a wind damage scale created by T. Theodore Fujita to classify tornadoes. The ratings are based on the amount and type of wind damage.

F-0 and F-1 tornadoes are considered "weak" and account for 69 percent of tornadoes.

F-4 and F-5 are considered "violent" and are the highest rankings.

What would an F-6 or greater tornado seem? The damage created would be "inconceivable," said a spokesman for the Weather Service.

Where to seek shelter amid threat

The first thing to do is learn the difference between a tornado watch and a tornado warning.

A "tornado watch" means conditions are right for a tornado to develop. Turn on a radio or TV and listen for further announcements --- even if the sky is blue.

A "tornado warning" means a tornado has been sighted by weather radar.

The watchword in tornado safety is "down." If your house or school has a basement, go there. If not, head for a closet or a bathroom.

Stay away from windows, and curl up so your head and eyes are protected.

If you're in a mobile home, the advice is different. Leave as quickly as possible. A mobile home is not as secure as some standard homes, and you run a greater risk of being injured by falling and flying debris.

If you're in a car or on the street, leave the car and take shelter in a building.

If no building is available or if you're in the country, take shelter in a ditch or ravine or behind the concrete pilings of an overpass.

Types of tornadoes
SUPERCELL TORNADO
It begins with an updraft inside a giant "supercell" thunderstorm. Then winds blowing in a variety of directions at various altitudes spin the updraft into a tornado.
NON-SUPERCELL TORNADO
It's the most common tornado in the Florida peninsula and the desert Southwest. Although it may pack damaging winds, it generally is smaller than its supercell cousin.
HURRICANE TORNADO
It is a spinoff of thunderstorms that form after a hurricane heads inland.
/ Knight Ridder Tribune

Tornado Alley?
Total tornadoes reported in Georgia counties from 1950 to 2000:
Map of Georgia shows counties color-coded to indicate
0-4
5-9
10-14
15-19
20+
Map of metro Atlanta shows total tornadoes for each county:
Bartow 20
Cherokee 15
Gwinnett 10
Hall 23
Cobb 24
Rockdale 6
DeKalb 10
Fulton 20
Douglas 8
Paulding 6
Sources: National Weather Service; Cherokee County Emergency Management Agency
/ CHUCK BLEVINS / Staff