Severe storms challenge weather sleuths

SUFFOLK—The debris had barely settled from last week’s storms when meteorologists fanned out across Virginia for an exercise in detective work.

The questions: Exactly how many tornadoes had touched down from the swirling mass of ugly weather? Where did those twisters go, and how strong were they?

The answers matter to scientists, emergency planners and even storm victims, said Bill Sammler, storm warning coordinator for the National Weather Service in Wakefield. But the facts can be elusive.

The clues lie in damage patterns, far-flung debris, tree bark and mud spatters. Even for experts, distinguishing weak tornadoes from other freaks of a storm “can be very complex, and every situation is different,” said Sammler, who has investigated about 30 tornado reports in his 14 years on the job. “You always have to go in with an open mind.”

The potent storms that slashed across the state last week offered a wide range of investigative challenges.

It did not take an expert to see that the storm that devastated parts of Suffolk was a tornado, Sammler said. It left a trail of flattened buildings; people took photos of the funnel cloud. “The stronger a tornado is, the easier it is to tell it’s a tornado,” Sammler said.

But where did the tornado go, and how strong was it?

Sammler and a colleague spent hours on Tuesday picking their way through devastated Suffolk neighborhoods and splintered stands of trees. They reviewed radar records. They caught a ride on a Civil Air Patrol plane for an aerial view of the damage.

Sammler concluded the tornado scoured the earth for at least 10 miles, from downtown Suffolk to the rural community of Driver. Then it withdrew into the sky, only to touch down in a greatly weakened state at the Norfolk Naval Station, 22 miles to the northeast.

Meteorologists at first had thought a separate tornado struck the Navy base. They made the link after finding strips of insulation from buildings in Suffolk a short distance from the base. By week’s end, they found evidence of nine other tornadoes, from Mathews County to Halifax County.

The tornadoes caused at least $32 million in damage and sent more than 70 people, mostly from Suffolk, to hospitals. No one was killed.

Earlier last week, weather service officials believed eight tornadoes had struck the state. But they raised the number late Friday after examining storm-scene damage.

The officials determined that previously unreported tornadoes had hit Greensville and James City counties.

They also decided that damage believed to have been caused by two tornadoes around the Gloucester-Mathews line actually stemmed from one tornado. And they ruled that a separate tornado hit southern Mathews.

The Suffolk tornado leveled so many well-constructed buildings that Sammler estimated it as a strong EF-3—a designation on the Enhanced Fujita scale suggesting winds of 160 mph. It was the strongest tornado to hit Virginia since a 1993 twister that killed four people and destroyed a Wal-Mart in Colonial Heights.

Sammler considered upgrading the Suffolk tornado to EF-4—the second-highest level of tornado intensity. But he hesitated because some homes in its path were still standing, albeit barely. An EF-4 probably would have flattened everything it encountered, he said.

Still, Sammler said, the tornado may yet enter the record books as an EF-4 after its data are reviewed by experts in the Midwest with more experience in big-league twisters.

In the Midwest, tornado investigators get lots of help from highly competitive TV stations and private “tornado chasers” who brave perilous weather for video and photos of twisters, said Jim LaDue, a meteorologist with the weather service’s Warning Decision Training Branch in Norman, Okla. But late-night storms still demand close looks, ideally from the air, he said.

A more challenging task in the Midwest is determining the strength of major tornadoes in the EF-3 to EF-5 range, “which is mostly art with a little science thrown in,” LaDue said. The severity of damage can depend on slight differences in the way a building is constructed and the direction it faces, he said.

Virginia averages 15 to 20 tornadoes a year, the vast majority of which are weak EF-0s or EF-1s with just enough strength to snap off trees and disassemble mobile homes, he said.

Weak tornadoes often cause the same level of damage as downbursts—sudden, downward surges of straight-line wind from severe thunderstorms. Distinguishing weak tornadoes from downbursts is the main challenge of Virginia tornado investigators.

Soon after the storm passed last Monday, Sammler drove to Brunswick County to examine some damage there, including a wrecked house. A hook-shaped radar image had suggested a weak tornado. He hiked through the woods and found a narrow, well-defined path of damage. Debris was scattered in several directions.

The verdict: a classic Virginia tornado.

Many people wrongly assume that twisted trees or metal prove a tornado came through, Sammler said. But straight-line winds can twist objects, too, as anyone knows who has watched video of a street sign shimmying in a high wind.

One of the best clues is damaged trees with bark missing, he said. Tornadoes exert a pulling force that yanks off bark; straight-line winds leave the bark alone while felling or uprooting the trees, he said.

Some cases are close, but Sammler always calls them one way or the other. Several years ago on the Eastern Shore, he decided a storm was not a tornado because it splattered mud on only two sides of a house in its path rather than on three or four sides. He figured straight-line winds would have splattered only one or two sides, whereas the spinning of a tornado would have splattered more.

The weather service conducts such investigations partly to try to validate the tornado warnings it issues, based on radar signatures, Sammler said. Accurate records of tornado strikes also help scientists track long-term weather patterns, and help local and state officials with emergency planning and the writing of building codes, he said.

Many storm victims appreciate knowing exactly what hit them, Sammler said. “I think knowing gives some people closure.”
Contact Bill Geroux at (757) 498-2820 or bgeroux@timesdispatch.com.