Age: 18, b-day is 8/27. Graduate of MLK High in Nashville, TN. Will attend MU in PA. Love football, soccer, Frisbee, Scouts, Science Olympiad.
By: Astrometeor , 3:11 AM GMT on May 04, 2014
The following has been transcribed from the Nashville NWS-WFO's page. Click here to be taken to source. The message is particularly aimed for anyone living in the southern Middle Tennessee region of the state.
Have you seen debris in your yard this week? It may be from the Lincoln County EF-3 Tornado!
We Need Your Help!
Did you see any debris in your yard this week?
It may have come from the Lincoln County Tornado!
On Monday April 28th, 2014, a severe weather outbreak across the lower Mississippi Valley and much of the southeast US resulted in multiple tornadoes spanning from the Louisiana/Mississippi border up into northern Alabama, Southern Middle Tennessee and northern Georgia. One such tornado occurred just south of the Nashville county warning area (in Huntsville's area) in Lincoln, County Tennessee which resulted in 2 fatalities.
Here is a map of the active weather period across the southeast US from April 27th - April 30th. The April 28th tornado outbreak is highlighted in red:
(fatalities are indicated by boxed numbers)
The Lincoln County EF-3 tornado was one that both the Huntsville and Nashville offices were watching very closely. While the Huntsville NWS office was busy tracking the tornado that was moving through Lincoln County, the Nashville office was preparing their warning and letting the emergency manager in Coffee County know that the city of Tullahoma was in the path of the tornado, should it continue to stay on the ground.
This is what the meteorologists at both offices were seeing in chronological order:
At 8:09 PM CDT, according to the NWS Huntsville damage survey (Found Here), the tornado touched down in extreme southern Lincoln county. Five minutes later at 8:14 PM, the radar first detected a Tornado Debris Signature (or TDS) on the KHTX radar in northern Alabama. You can see it on the right hand side of the picture as the little blue speck south of Fayetteville (see above).
The image on the left is traditional reflectivity, which tells the meteorologist about intensity of rainfall and/or hail within the storm. In classic supercells, the reflectivity structure looks much like a backwards comma. The comma head part of the storm is called the "hook echo" as indicated on the left hand side of the picture above. This is where the tornado would typically be found. With the recent upgrade to Dual-Polarization technology, the radar can see much more than before. On the right hand side, is the new Dual-Pol radar called Correlation Coefficient which can differentiate between rain, hail, or in this case, tornado debris. The lower the CC value, the more likely that it is NOT a meteorological target. In the above image, the very low CC values (indicated in blue colors among the purple), located within the hook echo, tells the meteorologist that this signature is most likely tornado debris and that a tornado is in fact on the ground at this time.
At 8:23 PM, or 14 minutes after the tornado touched down, the TDS signature (right) continues to be seen on the CC radar image. Also, the hook echo on the left shows dark red colors meaning that the objects within the hook echo are reflecting back to the radar very brightly. When the reflectivity values within the hook echo are in the reds or higher, it too indicates debris within the tornado. In fact, this signature is often called a "debris ball" since it looks like the comma head has a ball at the end of it. The CC signature is quite a bit larger than the previous scan, which means the tornado continues to intensify and becoming stronger as it moves northeast through Lincoln County.
At 8:33 PM, or 24 minutes after touchdown, the tornado begins to lift, ending its damage path in southern Moore County (again according to the NWS Huntsville damage survey). As can be seen in the reflectivity image on the left, the hook echo is not as defined as in the previous scan, indicating weakening in the circulation. The supercell is looking less like a comma and losing its overall structure. Good news for residents of Lynchburg and Tullahoma which were in the path of this storm! However, if you look at the CC image, the TDS looks even bigger and brighter than it had in the last two scans. Well, it can't be that the tornado is getting stronger and wider, because the survey concluded it had ended at this point. What could it be?
As it turns out, the debris associated with the tornado continued to be carried in the winds associated with the supercell. Although not shown here, the TDS was seen over 20,000 feet! At these heights, the wind field was over 50 knots from the southwest. So what happened here is the debris was lofted so high that it was beginning to get caught in the upper level winds and carried downstream into southern Middle Tennessee! So while on radar, it may seem like the tornado was getting bigger, it had actually dissipated and its debris was being carried by the winds to the northeast.
Now at 8:47 PM, it is becoming more clear what is happening. The supercell continues to deteriorate with the hook echo very small and moving north into southern Bedford County. The CC values on the right are not as deeply blue, although some pixels are still very blue but they are more spread out and broad than previously. The debris cloud is expanding to the northeast, which makes sense considering the winds at this height are strongly southwesterly. So while the debris cloud indicated on the CC radar image begins to expand into Coffee and Bedford counties, a phone call comes from the Coffee County EMA Allen Lendley...
"Hey there Nashville, this may sound strange but a volunteer fire fighter on the road outside of Manchester just reported that pieces of paper are falling from the sky. Do you know anything about what he is talking about?"
(*not a direct quote)
Why yes Allen, we might have an explanation for that!
Now here at 8:56 PM, 23 minutes after the tornado lifted and 47 minutes after it initially touched down in southern Lincoln County, the supercell has more or less fallen completely apart. The Nashville office has cancelled their tornado warning they issued for this storm due to it weakening and losing its velocity signature as well (not shown). However the debris cloud continues to spread out and drift to the northeast in the upper level winds. The cloud is beginning to enter southeast Warren County and approach the city of McMinnville. Preliminary reports from the McMinnville area have come in since Monday with reports of debris being found. This debris cloud would continue to drift northeast before dissappearing finally just before reaching Crossville!
The Nashville county warning area (all of Middle Tennessee excluding Franklin, Lincoln, and Moore counties) was lucky enough to avoid any tornado activity that evening. One tornado was confirmed earlier in the day in White County but for the most part, the Mid-State dodged quite a bullet on Monday night!
The NWS Nashville office has analyzed the debris signature on both KHTX and KOHX radars and have put together this subjectively analyzed map of where debris may have landed across southeastern Middle Tennessee. If you live in the area shaded yellow in the below image, you may have had some debris fall in your yard! In order for debris to be picked up and lofted this far, its most likely the debris you might find would be lightweight, like paper, envelopes, pictures, or insolation.
If you happen to discover something like this in your yard over the next week, PLEASE LET US KNOW! We are attempting to put together a map of debris fall based off your reports to correlate with the radar data so we can better understand how these TDS signatures can help us see what is happening in reality. Also, you might find something like someone's family photos that might want to be returned by the people who lost them. Hopefully we can return some of these lost items back to their owners!
If you find anything in your yard that you think is debris associated with the tornado, please submit a picture of the debris and either the GPS coordinates of where you found it, or the address information to our Facebook page, tweeting the information to our Twitter page(@NWSNashville) or emailing us at email@example.com.
We appreciate your help!
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