Photos by Kyle Green | The Roanoke Times

A damaged street sign and downed electrical wires were among the results of the twister.

About 10 homes were damaged by fallen trees, including this one on Rosalind Avenue, as well as up to six vehicles.

National Weather Service workers Phil Hysell and Anita Silverman determine the tornado's track during a survey Wednesday on Stephenson Avenue.

A tornado skipped through parts of Roanoke on Tuesday evening, the National Weather Service confirmed Wednesday.

It was weak, with winds no higher than 80 mph, and it cut a narrow swath, never wider than 60 yards. It lasted about three minutes, and the funnel was probably aloft more often than it was on the ground over the 1.4-mile-long damage path, said meteorologist Phil Hysell, who led a storm damage survey Wednesday conducted by the weather service's Blacksburg office.

But weak and sporadic as it was, the tornado caused an estimated $350,000 in damage, said Mike Guzo, Roanoke emergency management coordinator. Guzo said a preliminary estimate indicated that 55 properties were affected, with about 10 homes damaged by fallen trees, as well as up to six vehicles. The damage figure probably would not be enough to qualify the city for federal disaster assistance, Guzo said.

The tornado, which occurred about 7:30 p.m., first touched down near the intersection of Bluefield Boulevard Southwest and Welch Road, the National Weather Service determined, and skipped southeastward, finally lifting on Robin Hood Road.

The tornado was rated EF-0 on the Enhanced Fujita Scale of tornado intensity. An EF-0 rating, the weakest on the scale, denotes wind speeds of 65 to 85 mph. Hysell said estimated winds in Tuesday's tornado were 70 to 80 mph. The Enhanced Fujita Scale tops out at EF-5, tornadoes with winds of more than 200 mph that sweep well-constructed homes entirely off their foundations.

"All the characteristics of a tornado were there: a violently rotating column of air in contact with the ground," Hysell said. "It's just that the wind speeds weren't that strong."

In addition to video and photos of funnels that were shown by Roanoke media outlets, Hysell said three factors swayed him to the conclusion that it was a tornado and not straight-line winds or a microburst that caused the damage.

"First, it was a narrow path, which means it did not widen with distance," Hysell said. "Secondly, the damage did not diverge," he added, meaning that trees were not blown outward from a center point, as would be the case with a microburst.

"Finally, the trees did not lie along the path of the storm, but were lying slightly to the east of the storm motion," he said. Hysell noted many fallen trees pointed east or northeast, whereas the storm had been traveling southeast. This would indicate at least some weak counterclockwise rotation, throwing trees to the left of the storm's path.

Besides those hit by falling trees, few structures were damaged. Hysell said this may have indicated the funnel was aloft through much of its journey, with the stronger winds remaining in the tree canopy.

"It was not in contact with the ground through its entire life," Hysell said.

The tornado sprang from a supercell thunderstorm that developed over West Virginia and moved southeastward toward Roanoke, said meteorologist Anita Silverman, who followed the storms on radar at the weather service office Tuesday night and then joined Hysell on the damage survey Wednesday.

"It was a supercell," Silverman said. "It wasn't large, but it was a supercell."

A supercell is a rotating thunderstorm that is separated from other storms. Tornadoes and large hail occur in supercells more often than in other kinds of thunderstorms. Supercells, common in the central United States, especially in spring, are infrequent in Southwest Virginia.

Silverman said that a 7 p.m. weather balloon launch from Blacksburg indicated that the winds over Southwest Virginia were extremely favorable for storm rotation early Tuesday evening.

No tornado warnings were in effect when the storm hit Roanoke, but the National Weather Service issued a severe thunderstorm warning for Roanoke, Roanoke County, Salem, and parts of Craig and Botetourt counties at 6:59 p.m. The text of the warning noted rotation in the storm, the threat of high winds, and the possibility that a severe thunderstorm can produce a tornado with little or no advance warning, Hysell said.

The supercell continued southeastward toward Smith Mountain Lake and beyond, prompting several tornado warnings. No additional tornadoes or significant damage have been confirmed.

The ability to get warnings out was hampered when National Oceanic and Atmospheric Administration weather radio was knocked off the air. A phone line from the weather service office to the transmission tower site on Poor Mountain was inadvertently cut by a contractor on Monday, the National Weather Service said.

Verizon spokesman Lee Gierczynski said the phone company received a report of the cut cable Tuesday and dispatched a repair crew.

"They had to leave the site because of the severe weather," Gierczynski said. The crew returned Wednesday morning and completed repairs later that day, he said.

Tornadoes, while uncommon in Southwest Virginia, do occasionally occur in the area. An EF-1 tornado with winds up to 95 mph, damaging four homes, was confirmed in Franklin and Henry counties May 8.

The last confirmed tornado in the Roanoke Valley occurred Aug. 5, 2003, touching down briefly near Hollins, causing damage at ITT Night Vision and Sunnybrook Garage & Lawn Equipment.

A tornado April 4, 1974, injured six people and caused widespread structural damage through parts of Salem, Northwest Roanoke, Northeast Roanoke and adjacent Roanoke County. This was the last confirmed tornado in Roanoke city.

According to Tom Grazulis' historical reference, "Significant Tornadoes," three people were killed as two buildings were demolished by a tornado in Salem on April 24, 1896.

"Tornadoes have occurred in Roanoke County before, though not as often as in the Plains," Hysell said. "This should be a wake-up call."

Staff writer Cody Lowe contributed to this report.