The bad news is that it could happen again. The best news is that storms of this magnitude are extremely rare, and those in the path of the next one may have a few minutes’ more warning. The March 18, 1925 maelstrom—the longest on record—inspired a long, slow movement toward better tornado forecasting and warnings.

For years, the average lead time for warnings was only 6 minutes. Now technology has doubled it to 12 minutes—precious extra seconds in which to secure property and run for cover.

A BELOW-AVERAGE YEAR...SO FAR

To date, the year 2000 is coming in well below average for tornadoes in the United States: just 87 as of March 23, compared to the annual January-March average of 220. (Averages are calculated over the last three years.)

“Last year we had two big tornado outbreaks, one in Arkansas and the other in Arkansas and Tennessee,” says meteorologist David Imy of the National Oceanographic and Atmospheric Administration’s (NOAA) Storm Prediction Center in Norman, Oklahoma. “So far we’ve had fewer, especially in January.”

A cold period after the first of the year kept at bay the areas of unstable air mass and storm systems that normally move across the country. This helped keep the January tornado count down to just 16—compared to a January average of 104. A warmer February, with moist air pushing up from the Gulf of Mexico, brought twisters back with a vengeance, accounting for 49—ten more than the average. But with three-quarters of March gone, so far only 22 tornadoes have been spotted this month, compared to the March average of 77.

Such statistics are scant comfort to residents of Camilla, Georgia, the place officials say was “ground zero” in a February 15 outbreak that raged across four southwestern Georgia counties claiming at least 18 lives and injuring 100. It was the worst tornado devastation in the state in 56 years.

Other tornadoes this year have caused substantial damage and sometimes injuries in Texas, Louisiana, Arkansas, Alabama, Florida, and Wisconsin.

STEAMROLLERS IN THE AIR

What are tornadoes? How are they formed? And what should you do if you look into a dark gray-green sky and see a black funnel cloud headed your way?

Tornadoes are violently rotating columns of air extending from thunderstorms to the ground. They begin life as precursors of thunderstorms: vortexes of air whirling horizontally over the ground, like invisible giant steamrollers in the sky. They are originally set into motion by shifting wind directions and increases of wind speed with altitude.

As the thunderstorm forms, rising air tilts this steamroller on its end. That is how a tornado is born.

Some tornadoes are harder to see than others. The 1925 outbreak was so wide and hugged the ground so closely that people didn’t realized what it was until it was upon them. Tornadoes also may be obscured by rain—or may remain invisible until they begin picking up debris. Obviously, detection of such weather patterns is easier from the air, and geostationary satellites hovering over specific areas form important tools in NOAA’s forecasting arsenal. The Storm Prediction Center also uses Doppler Radar and computer models, in addition to old-fashioned eyeball observations, to stay on top of quickly shifting conditions.

TORNADO DEFENSES

To defend against a hurricane, for starters, experts advise having handy a NOAA Weather Radio with an audible alarm tone and a battery backup. The radio can be set to provide an automatic alert in case a tornado watch or warning is issued, even when the owner is asleep.

Swift movement to a planned shelter area, ideally a basement, is critical. If no underground shelter is available, the best plan is to move to an interior room or hallway on the lowest floor and get under a sturdy piece of furniture. If outdoors, individuals should get out of cars and lie flat in a ditch or other depression. Trying to outrun a tornado, even on wheels, is not recommended: The most dangerous places to be when twisters strike, according to NOAA, are in cars or mobile homes.

As for the 1925 outbreak, according to meteorologist Imy, “If it happened once, it could always happen again.”

Eye in the Sky is a weekly series that brings you the story behind the headlines using satellite imagery, remote sensing, aerial photography, and maps. This feature is developed by National Geographic News with the sponsorship of the National Imagery and Mapping Agency (NIMA) and Earth-Info. Check out maps and imagery at http://www.earth-info.org.