National Weather Service meteorologist Richard Kane pointed at a three-foot strip of missing bark on a tree -- stark white as if the branch had been washed clean -- and shook his head.

"This bothers me," he told his colleagues on the edge of a hill in Sheraden yesterday.

Uprooted trees, downed power lines and the twisted metal roof of a nearby shed, shredded into portions, were all part of a small and concentrated swath of destruction carved out by a tornado that touched down on Thursday in an area near Chartiers Avenue and DuBois Street.

The tornado, graded as an EF0, or the weakest on the Enhanced Fujita scale of tornado strength, was the fourth in the city since 1944. Tornadoes struck Mount Washington in June 1998 and again in June 2003. Before that, the previous twister to touch down in Pittsburgh was in Lincoln Place in 1944.

Mr. Kane and three other meteorologists were a part of a team that surveyed some of the damage in the Sheraden and Uptown areas to determine what sort of weather event had moved through during Thursday afternoon's severe storm.

While meteorology is an imperfect science, Mr. Kane and his colleagues have perfected the art of determining whether a bent chimney on top of a duplex in Uptown is the work of a microburst -- a strong downward blast of wind -- or a tornado.

In the case of Uptown, the damage appeared to be from a downburst that pushed 85 mph winds through the neighborhood, while in Sheraden the sight of trees with the bark sanded off their limbs indicated the work of a tornado.

Both carried the same general wind speed, but only one -- the tornado in Sheraden -- actually touched the ground and sustained enough momentum to twist metal and shear bark.

"If the siding is torn off in a particular direction and the wall is crumbling in the opposite direction, that tells us something about what happened there," Mr. Kane said after touring the ruins of a brick duplex in Uptown.

Reports of funnel cloud sightings were rampant on Thursday, when three lines of storms moved through, causing widespread wind damage and flooding. While it is not uncommon to see a funnel cloud with microbursts, the type of wind damage -- snapped tree limbs instead of the shorn limbs and uprooted trees of a tornado -- help meteorologists determine which happened.

The cyclonic nature of the wind damage in Sheraden, which included "projectile damage," suggests the winds were rotating violently, hurling objects such as tree limbs and other items off of the side of houses and cars.

This tornado may have been a "weakling," as Mr. Kane put it, compared to some of the Great Plains tornadoes, but that characterization doesn't minimize the potential for destruction.

"If you're not prepared and you're in the wrong place at the wrong time, you are definitely going to be in harm's way," said Zaaron Allen, a meteorologist with the weather service assisting Mr. Kane yesterday.

The investigators' walk-through yesterday was a combination of hard evidence, like walls blown over, and testimonials of residents.

Melanee Gist, of Uptown, roared at Mr. Kane was he walked by her stoop on Watson Street yesterday.

"That's what I heard," she said, perched near a utility pole that had been snapped in half. "Then I saw a big ol' white cloud. Everybody laughed at me when I told them what I saw."

Mr. Kane, with a straight face as he surveyed the damage, turned and shook her hand.

"Anything helps," he said.