Just like hurricanes, tornadoes can be categorized from an EF zero all the way to a destructive and devastating EF five. Despite them being categorized by wind speed, we actually can’t get an exact measurement of the winds, but we can get a pretty good estimate based on the storm damage.
Much of the time the destruction may look like a tornado has hit, but that may not always be the case. That’s where the storm survey team at the National Weather Service comes in.
The experts spend hours and sometimes even days assessing the destruction and coming to a conclusion on whether or not a tornado has hit, and if so, how strong it was. Justin Weaver, Meteorologist in Charge at the National Weather Service in Lubbock explains.
“There are some things you can look for as you move through the path of the tornado.“ Weaver says. “You can see the damage blown in different directions. So a lot of the time it’s a good indicator that it’s a tornado. Straight line wind damage or downburst damage tends to be more divergent where the damage is kind of blown in a fanning pattern and the damage kind of fans out. So that’s one thing we’ll look for if we can get aerial imagery of the path. Sometimes we can see that. So there’s all sorts of clues we look for.”
Once they determine whether or not it is a tornado, they proceed to determine its’ strength based on the level of damage that has occurred.
“If we’re out in the field and we see broken off tree limbs and broken tree trunks we think maybe 100 mph winds, something like that. If we see well built homes destroyed or the debris is blown away we think winds in excess of 200 miles per hour. Of course there’s a whole spectrum between the low end and that extreme damage. There’s been a lot of work done by wind engineers. A lot of that is done right here at Texas Tech University that helps us decide what kind of wind is expected to snap a tree trunk off, what kind of wind it takes, how high of a wind it would take to move the roof from a well built home.”
Unfortunately, because the strength of the tornado is solely based on the severity of the damage, if the event happens in a more rural area where less destruction would occur, they can’t verify the strength.
For more information on storm surveys click here.