How the tornado damage will be assessed

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Posted: Monday, November 18, 2013 7:08 am | Updated: 9:34 am, Tue Feb 4, 2014.

In a rare November outbreak of tornado activity five people have lost their lives and many more remain missing.  Scores of home have been removed from their foundations and power is out to tens of thousands. The Storm Prediction Center graphic below indicates over 80 tornado reports.  But how will the meteorologist determine which of the reports are real tornado touch downs, which are duplicate reports and which are reports of just strong wind?

Storm reports received by Storm Prediciton Center

Teams of meteorologists acting as part weather scientists and part structural engineers will depart from weather service offices across the Midwest to survey the damage. They will use all resources at their disposal including storm video, aircraft observation, photos damage patterns and a laptop that runs the official damage assessment software based on the Enhanced Fujita Scale.

Ted Fujita was a researcher from the University of Chicago who took special interest in damaging winds. He claimed his passion was born in studying the damage patterns resulting from the atomic explosions in his native Japan. In 1971 Dr. Fujita proposed a scale to classify the intensity and size of tornado's. The scale would take his name and become the basic tool for classifying twisters.

But weaknesses were discovered in the scale that could lead to subjectivity and ambiguity, two things scientists would rather not occur.  So an updated scale was developed that included classification based on the construction used in building, damage to vegetation, use of photos and a specific and rigorous computer program to determine damage patterns. Using the enhanced scale the teams will look for twenty eight separate damage indicators such as the type of connectors used in the framing of damaged structures and assess the severity of the damage on a scale of 12.  The complexity of the grading system is surprising to most who might have assumed that if a shed is damaged it is an EFO tornado but if a house is missing it is an EF4 tornado.  Image below give an idea of the how complex some of the assessment becomes.

Determining damage

Once the field teams finish their work and exact number of tornado's that touched down over the weekend will be issued.

John Scalzi

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