164 Rare Polarimetric Tornado Debris Signatures (TDS) in the Appalachian Region and the use of Remote Sensing Techniques to Assist with the 24 February 2016 EF3 Survey in Virginia

Thursday, 10 November 2016
Broadway Rooms (Hilton Portland )
Stephen J. Keighton, NOAA/NWS, Blacksburg, VA; and M. B. Sporer

Handout (6.3 MB)

On 24 February 2016 a tornado with a path length of 27 km produced EF3-rated damage across portions of Appomattox County, just east of the Appalachian Mountains in central Virginia. This tornado resulted in one fatality and seven injuries. It was just one of 17 tornadoes that occurred from South Carolina to Pennsylvania on this day, in a relatively rare February outbreak of severe weather for the mid-Atlantic region. This was only the third recorded tornado in Appomattox County since 1950, the strongest tornado since March of 1998 in the 40-county warning area (CWA) covered by the National Weather Service (NWS) office in Blacksburg, VA, and also the strongest February tornado ever recorded in the Blacksburg NWS CWA.

The EF3 that occurred during that afternoon was at relatively long ranges from any WSR-88D radar (~140-170 km), which were viewing no lower than about 3000 m above the ground.  Nevertheless, impressive radar signatures included a Polarimetric tornadic debris signature (TDS) seen in WSR-88D dual-polarization data from both the KFCX and KAKQ radars, as well as a notable low-level rotational track signature with an increasing trend seen in multi-radar multi-sensor (MRMS) products, which are still relatively new to operational forecasters.  Given the distance of this storm from the radars along with some data ambiguity issues associated with this range, these signatures allowed for a confident tornado-warning decision as well as confirmation of tornadic debris.

A second example of a Polarimetric TDS was more recently observed in the central Appalachian region, this time on the west slopes of the mountain chain on 21 June, 2016 from the KRLX WSR-88D, and at a range of about 95 km. An EF1 tornado was confirmed to have tracked for about 9 km in the complex terrain of West Virginia at elevations ranging from 900-1100 m. Given this was a remote area in the National Forest, the debris would have consisted only of trees and limbs, but the debris was still detected as high as about 2000 m above ground level by the radar.

Finally, some emerging remote sensing technologies were used to assist with damage survey for the 24 February EF3 tornado. Most notably, an unmanned aerial system (UAS or “drone”) was used to enhance the ground-based survey in more remote areas. An example of high resolution satellite imagery that can be obtained post-event and by request will also be shown for this particular tornado damage swath.

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