When severe storms occur-there’s likely going to be damage. In the worst storms, when faced with downed power lines and trees, the first thing most people think of is “was this a tornado?”
Here in the Lowcountry, most of the times that answer is no.
“In a year we might issue 150-250 severe storm warnings in a year, a good, active year versus less than a dozen tornado warnings,” says Ron Morales from the National Weather Service office in Charleston.
Rare but not uncommon. So how do we determine if a storm was tornadic or not? Looking at velocities on radar to find rotation is the first step, and that’s where the warnings come from. But a warning does not confirm a tornado. That only comes with verification from spotter video, or by damage surveys done by the National Weather Service after the storm has come and passed.
“Verification is a big weight on our shoulders if you will, we have to verify every warning we push out- whether it’s a winter storm warning or a tornado warning, or a flash flood warning-they all have to be verified.”Ron Morales, NWS Charleston
Most of the times that verification comes from damage surveys, in which meteorologists from the NWS office will go out and observe damage from a storm.
“(Storm surveys) are usually reserved for tornadoes, they can be for widespread events that got a lot of media coverage, lot of damage or even deaths. We know there’s damage, we know where we’re going, it’s a question of if it was truly tornadic wind that did the damage or straight line winds that did the damage.”
The way they verify that is by looking at patterns that the damage will be in.
Straight line wind damage would generally be unidirectional, with trees and debris all facing one direction as winds rush out ahead of a storm.
Compare this to damage caused by a tornado, which tends to be chaotic. Due to the characteristic spin, trees will fall in a convergent pattern. Both falling inward to the path of the tornado, but one following another in a straight line. In fact, surveys can tell the path and the distance of a tornado by this damage.
It is a process but it is a process that helps the National Weather Service improve their warnings by understanding exactly what happened.
Storm Team 2 Meteorologist David Dickson