The violent windstorm that struck Northeast Baltimore and Parkville early Wednesday briefly produced a tornado with top winds of 85 to 100 mph, the National Weather Service said Thursday.
The twister was rated an EF-1 on the Enhanced Fujita Scale, the second-lowest ranking.
The tornado was on the ground for less than a minute. Much of the damage done along the storm's five-mile path, from Morgan State University in Baltimore to Gunpowder State Park in Baltimore County, was caused by powerful straight-line winds, according to experts from the weather service's Baltimore- Washington Forecast Office in Sterling, Va.
In all, the report said, "it took only four minutes for the [storm] to accomplish its five-mile path of damage."
James E. Lee, the meteorologist-in-charge in the Sterling office, said such severe weather in November is an oddity for the area.
"And in the middle of the night in November? That's a double whammy," Lee said. "It kind of goes with our record-breaking snowfall and record-breaking heat" in 2010.
The findings were issued after an assessment of the damage, a study of the radar data and a review of aerial and security photos. The survey team concluded that the tornado formed within a line of thunderstorms that stretched from Pennsylvania to North Carolina. It crossed Maryland at 70 mph, striking Baltimore at 1:35 a.m.
Convection within a thunderstorm drew a jet of high-altitude winds to the ground, blowing a gap in the squall line, Lee said. That also created the rotation that became the tornado.
The ground survey found the tornado damage began at the western edge of the Morgan State campus. Its path through the Dutch Village apartment complex, where three units lost their roofs, was just one-tenth of a mile long and 175 yards wide.
From there the twister jumped a half-mile to the north. It touched down again and tore a path one-third of a mile long and 250 yards wide, centered on the Perring Parkway Shopping Center in Parkville.
There, security cameras provide important evidence of rotating winds. Debris close to the camera blew one way, while a shopping cart farther away rolled the opposite way, Lee said. The pattern of fallen trees and light poles, "leaf spatter" and eyewitness reports all contributed to the conclusion that the damage was caused by a tornado.
But along the rest of the storm's path, the damage was attributed to straight-line wind caused by the downburst of high-altitude winds.
Lee said the storm is a reminder of the value of NOAA weather radios. They would have awakened residents at midnight with a severe storm watch, and again at 1:04 a.m. when a severe thunderstorm warning was issued for Baltimore and the surrounding counties.
"That's a huge lesson," he said. "We can't say enough about the life-saving nature of that."