National Weather Service rates tornado touchdowns in Missouri

Mid-Missouri endured several tornado touchdowns late last week as severe storms rolled through on Friday, and the National Weather Service says they may not be done counting.

As of Monday afternoon, six tornadoes have been confirmed from Friday's storms: two in Benton County, three in Morgan County, and one that touched down in southern Boone and Callaway. All were rated at EF0 or EF1 strength, indicating minor damage to trees and buildings.

The Enhanced Fujita (EF) scale, used by survey crews to rate tornadoes, was developed over decades in coordination with engineers and meteorologists to better estimate tornadic winds from the damage produced.

"It's those wind speeds that we ultimately assign as the indicator for that tornado," says Steve Runnels, the Warning Coordination Meteorologist at the National Weather Service office in Springfield.

Steve says that surveying tornadoes is a lot like detective work. "So as we go in, we look at the debris, we look at anything that any eyewitnesses can tell us, and try to put the two and two together and play detective and try to figure out what most likely occurred," Steve explains.

Their investigation involves determining whether damage is caused by a tornado or by straight-line winds, which leave distinct damage behind. "In the case of the storm that was north of Gravois Mills yesterday, we saw windows broken, and that just is not a customary, straight-line wind event," Steve says.

Tornadoes also produce recognizable debris patterns, even when they are weaker. "These are weaker tornadoes that are moving at 50mph. And that results in the majority of the damage being on the eastern flank of that storm and less damage on the western flank," Steve explains. In contrast, straight-line winds will push wreckage in a single direction, while stronger tornadoes spread debris in all directions.

One of the most famous examples happened in Missouri almost 15 years ago. "The Joplin tornado," Steve says, "Just a monster storm. And in that storm, you could see debris going to the west, north, east, south. You have a clear-cut, rotating damage path." The Joplin tornado would ultimately be rated a catastrophic EF5 tornado that changed weather communication forever.