Twister prediction still guesswork

Modern technology improves the odds

Saturday, April 21, 2007

By RON JENSEN

The Register-Mail

GALESBURG - When the clouds boil with darkening shades of black and blue and green and the winds begin to hum, meteorologists start to sweat.

They measure in minutes - the time between commercial breaks on your favorite TV show - their ability to warn people that a tornado is barreling down on them. A dozen minutes can save dozens of lives.

"That is a responsibility that I take very seriously," said Terry Swails, chief meteorologist for KWQC-TV in Rock Island.

He said 12 minutes is an average lead time to tell people they may be in a tornado's dangerous path, a short amount of time, but a great improvement over just a few years ago.

"If we had three to five minutes, that was pretty good," he said.

Forecasting tornadoes is a critical task for a weatherman. But it is never easy and the decision to issue a warning is the culmination of hard data and experience resulting in an educated guess.

Swails said tornado warnings are followed by verified tornado sightings only about 55 to 60 percent of the time.

"Tornadoes are random events," explained Dan McCarthy, warning coordination meteorologist at the Storm Prediction Center in Norman, Okla. "We still don't know why one supercell storm will produce a family of tornadoes and another supercell will not produce any."

Kirk Huettl, a meteorologist with the National Weather Service in Lincoln, said only 20 percent of supercells produce tornadoes.

Tracking tornadoes

The weather forecasters are aided by the latest technology. Doppler radar, developed for miltary use, but ubiquitous for the past 10 or 15 years in weather stations, offers to trained eyes a snapshot of the ever-changing storm - its swirling winds, chaotic shears and bouncing updrafts. Enhancements to Doppler radar in recent years allow forecasters, in Swails' words, "to get down in that storm and look at that storm precisely."

From that, they can make their best estimate on whether a tornado is about to form and where. But it is still a gut-wrenching guess.

"The most difficult tornado to forecast is the first one," said McCarthy.

If a storm spawns one twister, it is more likely to spawn others, he said.

The first successful tornado forecast took place at Tinker Air Force Base, Okla., in 1948, according to a new book by author Nancy Mathis.

"Storm Warning: The Story of a Killer Tornado" is about the massive tornado that rocked Oklahoma City on May 3, 1999, claiming 48 lives and destroying and damaging thousands of homes, the largest tornado to ever hit a city. But the book, published last month, also describes the evolution of tornado forecasting.

"From the turn of the century until the early 1950s, the Weather Bureau actually banned the word 'tornado' from its forecasts," she said in a telephone interview from her office in Maryland. "It really took a couple guys from the Air Force ... before the Weather Bureau changed its mind."

The Weather Bureau feared forecasts of tornadoes would cause panic, she said. Also, there were worries that investors and developers would stay away from the Great Plains because of the tornado threat.

Plus, there was just no way to accurately predict when a storm was going to shoot off a twister.

The history of forecasting

But on March 25, 1948, Air Force Capt. Robert Miller and Maj. Ernest Fawbush saw similarities between an approaching storm and one that a few days earlier had spawned a tornado that did $10 million damage to the base. They informed their general, who, essentially, ordered them to forecast a tornado for the base.

"You're about to set a precedent," he told them, according to Mathis' book.

To the amazement of Miller and Fawbush, another twister skipped through the base a few hours later.

The civilian-run Weather Bureau became interested as the two uniformed forecasters continued to make successful predictions of tornadoes. Within a few years, the Weather Bureau was making tornado warnings, giving the public a heads-up about the storms that had been killing hundreds annually.

"The Cold War was a boon for tornado forecasting and research," Mathis said.

The same radar used to detect Russian bombers heading to the U.S. could give meteorologists an advanced look at coming storms. And sirens and bomb shelters, designed to warn of those advancing bombers and provide protection from their payloads, were quickly adapted for use during storms.

Improvements continue to protect the public from the killer storms. A recent upgrade in computer software allows the NWS to ignore political boundaries, like county and state borders, when warnings are issued, said Huettl. The warnings have greater specificity, such as placing the northern half of Knox County on alert rather than the whole county, limiting, Huettl said, the "crying wolf" aspect of a county-wide warning.

"People want to know what towns are in the path and when they are going to get hit," he said.

And that's the point of the forecasts. As much as tornadic storms race the blood of forecasters, they can simply terrify the public.

Tornado forecasts may be an inexact science or an imperfect art, whichever description you choose, but they have been effective since becoming common more than 50 years ago.

"Nineteen fifty-three is the last year a single tornado killed 100 people or more," Mathis said. "Before that, it was fairly common."