Another Tornado Debris Signature Caught on WSR-88D: Near Raleigh, NC

An apparent brief touch down of a tornado in Central North Carolina yesterday evening was detected by the Raleigh, NC WSR-88D Radar. The RDA was fairly close to the storm with the 0.5 degree beam altitude only around 1390 feet.

While the NWS survey has not yet been completed,  it appears this will very likely be an EF0 or EF1 tornado, based on the damage reported, photos and radar data.

Update 2:10 PM EDT: NWS just confirmed EF0 with 85mph winds.  Path length 1.25 miles / 150 yards wide 

The 22:31:59Z volume scan had a small, but defined TVS with gate to gate shear of ~81kts (+57/-24) and a well defined hook echo. It also developed a significant correlation coefficient minimum which was co-located with a reflectivity maximum in the hook where the TVS was also centered.

All of this convinced me, that there was indeed a tornado on the ground and in progress.   I quickly put together a “tweet” and sent it out at 22:36Z indicating that we now had a tornado on the ground.

I also submitted something to the effect,  on RAH NWSChat,  about a possible debris ball developing on radar.

Shortly there after we started receiving verification of damage and sightings of the tornado.

This is another example of how useful the Dual Polarization data can be when looking for Tornado Debris Signatures. Even for locating relatively “weak” tornadoes. Looking at the dual polarization data, it appears the “debris” was lofted to an altitude of around 2600 feet. My thinking is that much of this “debris” is likely tree leaves & foliage from the wooded areas where the tornado crossed, as well as, some other materials.

Click images to enlarge

Next Volume Scan shows "Debris Ball" with reflectivity maxium and correlation coefficient minimum, but velocity couplet weakening indicating tornado dissipating.

Photos of the wall cloud ( Credit: WRAL)

Damage to a home in Youngsville, NC

Tornado wind speed as it relates to force and damage potential: A case for an expansion of the EF scale?

With mobile Doppler radar units that have become available in the past 20 years that have extremely high resolution, we have been able to discover tornadic wind speeds in a few of the sampled tornadoes that have approached or in one case exceeded 300 mph. The recent El Reno tornado on May 31st, 2013 was another example of one of these.

Since the force of the wind does not grow linearly, rather it is squared (wind speed^2), these extreme wind speeds over 200 mph can cause unbelievable destruction. Since the kinetic energy is in the same arena as a small nuclear bomb, should one of these  ”Super Twisters” hit a densely populated urban environment the destruction would be exponential compared to a lower category tornado.  I created a graph to try to visually demonstrate the energy release or damage potential of the 2013 El Reno tornado as compared to just a few other recent tornadoes that have had good NWS storm surveys and tornadoes that had mobile Doppler radar measurements. There is a cluster of  Super Tornadoes in the upper right hand portion of the graph that illustrates how much more destruction they can create than an EF3 or EF4 tornado if they encounter buildings, cars or people.

I think it also illustrates that there is a huge range in the EF5 scale. Maybe now that we have entered the era of reliable remote sensing and we know there are tornadoes with wind speeds near or even above 300mph and the energy release is so much greater than a 201 mph EF5 tornado, the idea should be at least entertained about adding an additional(s) EF categorie(s) to account for these rare, but extremely violent tornadoes given the their potential destruction and design limits required to survive them.

Click graph for larger image


Remarkable radar data from the El Reno EF5 Tornado.

The May 31st EF5 El Reno Tornado that killed several storm researchers was sampled by ground based mobile X-band doppler radar (RaxPol) with very high resolution and found extreme wind speeds of almost 300 mph and rare satellite tornadoes. Other conventional fixed based NWS and FAA radars also captured remarkably  high velocities and signatures.

Below is the Terminal Doppler Weather Radar from Oklahoma City (TDWR). A C-Band Radar with a high resolution receiver  (250 meter resolution data displayed) and it appears to capture an apparent reflectivity minimum in the center of the tornado at the *exact* same time that the RaxPol indicated the same feature in the tornado. This is quite remarkable considering the distance from the radar is 26 miles. This reflectivity minimum is likely caused by descending air within the tornado and centrifuging of debris and precipitation in this case.

This is the RaxPol image from the exact same time as the TDWR image above.

RaxPol Mobile Doppler Dual Polarization Radar

The National Weather Service WSR-88D in Norman, OK recorded some of the fastest winds I am ever aware of. I am quite sure these winds are legitimate.  Below is a screen shot of  the tornado at 23:24Z

NWS KTLX Radar indicating maximum winds of 224 mph.


El Reno Tornado before it became extremely large and wrapped totally in rain. Courtesy of  Justin Drake @JustonStrmRider