Tornado or straight line wind damage?

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According to the National Weather Service Peachtree City the widespread damage on Saturday, July 21 was caused by straight-line winds, not a tornado. 

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Saturday, July 21 was a FOX 5 Storm ALERT Day as a powerful line of storms blasted north Georgia between 2 a.m. and 8 a.m. Given the extensive damage caused by the storms, The National Weather Service Peachtree City (NWS), did conduct a damage survey in parts of Gilmer County to better understand what happened.

Meteorologist found that most, if not all, of the damage, was caused by straight-line winds exceeding 70 mph which is close to hurricane force winds. The estimated peak wind of 85 mph occurred near Ellijay with a path width of 3 miles and path length of 5 miles.

To put this in perspective for you, the National Hurricane Center recognizes 74-95 mph winds as a CAT 1 hurricane, “Very dangerous winds will produce some damage: Well-constructed frame homes could have damage to roof, shingles, vinyl siding and gutters. Large branches of trees will snap and shallowly rooted trees may be toppled.

Extensive damage to power lines and poles likely will result in power outages that could last a few to several days,” so it’s no surprise that this area had widespread/significant wind damage, localized flash flood and continuous cloud to ground lightning.

Gilmer County wasn’t the only area that experienced storm damage from this storm system and because of the large swath of damage across the area, the NWS believes that the damage was caused by a “derecho.”

By definition, if the swath of wind damage extends for more than 250 miles (about 400 kilometers), includes wind gusts of at least 58 mph (93 km/h) along most of its length, and also includes several, well-separated 75 mph (121 km/h) or greater gusts, then the event may be classified as a derecho.  

In this case, the NWS estimates a wind swath of at least 350 miles long (Storm began in northern Kentucky). 

In addition, the NWS did mention that they cannot rule out the possibility that small short track tornadoes were embedded within the line of severe thunderstorms. However, finding individual tornado tracks within such a large scale wind event is very challenging. 

For the official damage survey click here


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