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Enhancing the Fujita Scale

Posted at 1:05 PM on May 28, 2008 by Craig Edwards (3 Comments)

Upon the completion of my entry level internship with the National Weather Service in Milwaukee, I was assigned to be the program leader for severe weather preparedness in Indianapolis in April 1976. My first task was to pour through a stack of newspapers about a foot high to determine the storm track and intensity of seventeen tornadoes that occurred in Indiana in March.

My assessments were based on field reports from observers and emergency managers, communicated via the print media. The Fujita-Pearson scale was developed in 1971 and my job was to determine the tornado's intensity, along with a path length and width for historical documentation. The storm data report also encompassed a narrative of the damage and an estimated dollar loss.

Allan Pearson, the Director of the Severe Storm Center at the time, worked with Dr. Ted Fujita to create this rating scale. This scale was updated by a collective group of individuals to define the intensity based on actual assessment of property damage. There are currently 28 indicators that can be used to estimate a tornado's wind speed.

Original work done by Dr. Fujita

In May of 1999, I was part of the NOAA assessment team following the devastating tornadoes in Oklahoma and southern Kansas. I have personally seen the damage caused by an F5 tornado, where cars were wrapped around trees and in some cases pavement and sod stripped from the earth's surface.

Earlier this spring I sat in on a presentation by Tim Marshall, who was on the team to devise the Enhanced Fujita Scale. Tim suggested in his seminar that Dr. Fujita, prior to his death, knew the scale needed some re-evaluation.

Enhanced Fujita Scale and damage indicators
CE

Comments (3)

In one of the weather-head mailing lists I'm on, there's been a lot of talk about Mr. Marshall's presentation and what to do about building codes. You probably remember the part in his talk where he showed "sliders," homes which were simply pushed off their foundations. There is a picture on the Star Tribune's web site which shows two houses pushed to the right off their foundations into a little pond. This is a great example of these sliders.

Also with those pictures, a co-worker of mine noticed the low walls of the foundations of those two houses. If she saw those right (and I think she did), there wasn't really any basement to those houses; they were basically on slabs, especially the upper house.

And yet another thing - houses are built nowadays with a high profile - two story houses are the norm, and many have 3 stories (if you include a walk-out basement). Those houses provide a much greater cross-section to the wind, and the force of the wind increases with the square of the wind speed. Or, given the same wind speed, the force is quadrupled for a doubling of area.

I hope that some good comes out of the disasters here - enhanced building codes and the enhanced enforcement of them.

But that's just what I think. Your mileage may vary.

Posted by Chris B. Critter | May 28, 2008 9:58 PM

Where did Tim Marshall speak in Minnesota? Is the speech available online?

Posted by Kiel Conrad | May 29, 2008 12:50 AM

We are about to interview Tim Marshall on Jet Streaming this morning. You can hear the podcast later today at:

http://minnesota.publicradio.org/radio/podcasts/jet_streaming/

PH

Posted by Paul Huttner | May 29, 2008 9:49 AM

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