Forensic meteorology - dissecting Sunday's tornado
Monday and Tuesday, cleanup and surveying was underway for East-Central Indiana and West Ohio counties, after an EF-2 tornado destroyed homes, barns and factories.
It is the job of the National Weather Service to survey the areas impacted by the tornado, and determine the strength, wind speed, and width of the tornado, and of course, its path. Meteorologists from three branches of the National Weather Service surveyed the tornado damage that occurred in their designated areas. They use an iPad app which allows them to rate the damage at each spot, and make pins to show the tornado's path. They add pictures from each spot they survey, which comes in handy later down the road.
Warning Coordination Meteorologist for Northern Indiana, Michael Lewis, explains "what this requires is just driving, stopping, plotting, charting, identifying what kind of damage and the level of damage. And you do that for every point along the way as you start working your way through. So it really is boots on the ground forensic evidence. It's like forensic meteorology".
From the survey, they determined that the tornado took a thirty-nine mile path from Deleware County, Indiana to Mercer County, Ohio. At each damage point, the NWS used a scale that correlates the wind speed that is needed to cause a certain amount of damage to a structure. They found that the max wind speed was 134 mph.
After each NWS branch put their observations into the iPad app, they participated in a conference call to make sure they all agreed. "We had a conference call to say, did the points look reasonable? Looking at the pictures, did the damage seem reasonable? Was that degree of damage and wind speed appropriate for what we were seeing the pictures? And then we agreed that it needed to upped, raised or lowered. And then we worked on tweaking the path so that we could say looking at the radar and from the field reports, this is where the storm actually tracked is it went up to the north and east," disclosed Lewis.
Thanks to advanced technology and storm spotters, finding the EF-rating is much easier now than it used to be.