News : \'Definitely a tornado:\' National Weather Service expert describes Sunday storm

The storm that heavily damages several blocks in Vinton on Sunday morning was "definitely a tornado," most likely an F2 with winds between 130 and 150 mph that lasted just 15-25 seconds, says Donna Dubberke of the National Weather Service.

Dubberke is the Warning Coordination Meteorologist for the National Weather Service Quad Cities location in Davenport. She joined other NWS weather experts and local leaders in touring the area near the houses and apartment buildings damaged or destroyed.

The tornado caused a damage path approximately 100 yards wide, said Dubberke.

Convergent vs. Divergent

In assessing damage, says Dubberke, the NWS looks for the extent of the damage as well as whether the damage is convergent (gathered together) or divergent (spread around). In a tornado, the lifting action of the storm tends to cause damage to be convergent on the ground. Later as the storm whirls away, it will cast debris in many directions. Evidence of that was found in the many boards which were hurled into the ground, or through siding and windows.

In a straight line wind storm, says Dubberke, the effect of the wind is to blow debris away from the damaged structures.

Despite technology, human eyes still essential to storm safety

The NWS will continue researching the storm, comparing the damage path to what its radar records show.

Dubberke explained, however, that even with the most advanced radar technology, it's very difficult to determine exactly what a storm that appears on radar will do on the ground.

"Our radars only see at 5,000 feet," Dubberke explains. "They can't see what is actually on the ground."

For that reason, says Robert Spangler of the Benton County Emergency Management office, there is a need for trained weather spotters who can identify storms from street level.