Monday, February 05, 2007

DEADLY DAMAGE




Our thoughts and prayers are with the victims of last week’s deadly tornadoes in Central Florida. The tornadoes hit at the worst time – early morning. Georgia has some experience with this kind of dangerous weather. It was just four years ago that Albany was visited by a killer twister in the pre-dawn hours in March. That was the same neighborhood that was hit in February 2000. I remember going down there in March 2003. The Iraq War had just begun the night earlier and as we approached the city of Albany, I saw the astonishing sight of a row of pecan trees laying on their side. Then I witnessed the heart-breaking sight of slabs where homes once stood. It’s sometimes all too easy to take a clinical look at destruction from the safe confines of the studio and it really jarred me to see what blobs of red obscure on a radar screen.
Storms that hit like that are a reminder that everyone should have a NOAA weather radio. These relatively inexpensive devices blare in the middle of the night when a tornado warning is issued. We want people to watch TV, but let’s face it – when its 2 am, you’re asleep. Your first reaction when you hear thunder might be to turn on the TV, but an alarm would get your attention faster.
The word tornado conjures up images of terrifying destruction, but not every tornado creates the same kind of damage. In the early 1970s, a professor from the University of Chicago sought to categorize the specific damage caused by different tornadoes. The Fujita scale, named after the fames researcher Dr. Ted Fujita estimates the wind speed with the damage. You’ve probably heard us say on TV that there was an F3 tornado in such-and-such a place.
In recent years, there has been a movement to update this venerable scale to more accurately take into account the kind of damage that different tornadoes do. For example, if a roof is blown off a strongly-constructed home, the damage might be classified as F1, but if a mobile home is destroyed, it might be considered F2.
Researchers at Teas Tech devised a new scale, which went into effect on February 1, 2007. The tornadoes in Florida are the first to be assessed using the new scale. The Enhanced Fujita scale is designed to more accurately rate tornadoes because it not only estimates the wind speeds, but also takes into account the kind of materials affected by the storm and the construction of the structures damaged by the tornado.
When using the new EF-Scale to determine the tornado’s EF-rating, meteorologists begin with 28 Damage Indicators. Each one of these indicators has a description of the typical construction for that category of indicator. Then, the next step is to find the Degree of Damage (DOD). Each DOD in each category is given and expected estimate of wind speed, a lower bound of wind speed and an upper bound of wind speed.
So for example, a tornado moves through a neighborhood and walls are knocked down of an area of homes. Here the Damage indicator would be #2, One or Two Family Residences (FR12). The typical construction for this fits being a brick veneer siding home. The DOD would be a 9, most walls collapsed in bottom floor. Thus, the estimated winds would be 127 - 178 mph with the expected wind speed of 152 mph. Now, taking this number to the EF-Scale, the damage would be rated EF-3 with winds between 136 - 165 mph.

The Feb 2 tornadoes break down as follows:
EF3 – Villages/Lady Lake area with winds of 155 to 160, claiming 7 lives with numerous mobile homes destroyed.
EF3 – Lake Mack/Deland area with winds of 160-165, claiming 13 lives with mobile homes destroyed and trees uprooted.
EF1 – New Smyrna Beach area with winds of 100-105, damaging roofs, collapsing chimneys.

For more information on the new scale and the indicators, go to http://www.spc.noaa.gov/efscale/ef-scale.html.

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