26 December 2012 HSLC Tornado near Beaufort, NC

A previous CIMMSE post outlined the potential for severe weather on 26 December 2012.  Instability was the key limiting factor in this event which produced one tornado in the MHX CWA four miles north of Beaufort with EF1 damage.

Numerous mesocyclones/velocity couplets were observed off the coast where instability was markedly greater, however most couplets dissipated prior to/just after moving into the more stable onshore airmass. A LAPS sounding located near KMRH at 19 UTC (Fig. 1), approximately one hour prior to the tornado touchdown, noted weak instability (barely negative lifted index, nearly 300 J/kg CAPE) and very strong shear. The sounding indicated 50 knots at roughly 2000 feet with 0-3km storm-relative helicity of 306 m²/s². LCL heights were also very low, around 400 feet, implying low level rotation would not need to  stretch far to reach the surface. Brandon Vincent of RAH forwarded along several archive RAP soundings centered at KMHX (about 11 miles west of KMRH) which also indicated very low LCLs (approximately 500 feet) with 0-1km storm-relative helicity of 350 m²/s² after adjusting the hodograph for observed storm motion.

LAPS 19Z KMRH 122612

Figure 1: 19 UTC LAPS proximity sounding centered near KMRH.

Earlier in the afternoon, around 1620 and 1730 UTC, two persistent velocity couplets off the Pender County/Onslow County coast moved onshore over North Topsail Island across Sneads Ferry and into Camp Lejeune. A KMHX radar loop of the 0.5 degree slice is given below (Fig. 2) which illustrates the strong rotation signature from the second couplet. Neither areas of rotation produced damage after extensive follow-up with Onslow county and Camp Lejeune emergency managers.

KMHX 0.5 loop 1730Z 122612Figure 2: KMHX 0.5 degree loop of base reflectivity (top left), base velocity (top right), storm-relative velocity (bottom left), and GR2Analyst normalized rotation (NROT) product (bottom right).

The Beaufort tornado was unlike previous storm cells of the day in that it did not have a persistent velocity signature offshore. Instead, a large circulation formed off the coast and produced straight line wind damage from Atlantic Beach east to Fort Macon, then north into downtown Morehead City (Fig. 3). The circulation then strengthened and produced an EF1 tornado about 4 miles north of Beaufort. The 0.9 and 1.4 degree slices (Fig. 4 and 5) are also available below.

KMHX 0.5 slice - Beaufort TornadoFigure 3: KMHX 0.5 degree loop of base reflectivity (top left), base velocity (top right), storm-relative velocity (bottom left), and GR2Analyst normalized rotation (NROT) product (bottom right).
KMHX 0.9 slice - Beaufort TornadoFigure: KMHX 0.9 degree loop of base reflectivity (top left), base velocity (top right), storm-relative velocity (bottom left), and GR2Analyst normalized rotation (NROT) product (bottom right).
KMHX 1.4 slice - Beaufort TornadoFigure 5: KMHX 1.4 degree loop of base reflectivity (top left), base velocity (top right), storm-relative velocity (bottom left), and GR2Analyst normalized rotation (NROT) product (bottom right).

The tornado caused tree damage and minor house (window and roof) damage consistent with EF1 damage and winds estimated around 90 mph. The tornado was on the ground for approximately 1/4 mile with a maximum width of 100 yards. One of our lead forecasters was unfortunately impacted by the tornado with several tops of trees broken off and a few large downed pine trees. He was sleeping just prior to the tornado, resting from working the previous midnight shift, and awoke to his wife yelling “get in the hallway!”. Thankfully no injuries or fatalities were observed with this tornado.

Beaufort Tornado - Roof Damage

Beaufort Tornado - Window damage

A closer look at the Dual-Pol data from 26 December 2012.

In reply to comments that Jonathan posted, below is a loop of the KMHX Dual-Pol radar imagery at 0.5 and 0.9 degrees (BR, BV, ZDR, and Correlation Coefficient (CC) [RHO in GR2]) over Camp Lejeune from 1731-1750 UTC.

KMHX Dual-Pol data at 0.5 degrees for Onslow County

KMHX Dual-Pol data at 0.5 degrees for Onslow County

KMHX Dual-Pol data at 0.9 degrees for Onslow County

KMHX Dual-Pol data at 0.9 degrees for Onslow County

The tornado debris signature was observed with the confirmed EF1 tornado north of Beaufort. Below are two images at the 0.9 degree level (0.5 degree slice was too noisy due to close proximity to KMHX radar) from 1952 and 1956 UTC.

Beaufort Dual Pol TDS 1952 UTC

Beaufort Dual Pol TDS 1952 UTC

Beaufort Dual Pol TDS 1956 UTC

Beaufort Dual Pol TDS 1956 UTC

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About David.Glenn

General forecaster with NWS Newport/Morehead City, NC. State Coordinator for the Community Collaborative Rain, Hail, and Snow network (CoCoRaHS).
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2 Responses to 26 December 2012 HSLC Tornado near Beaufort, NC

  1. Jonathan Blaes @ WFO RAH says:

    Thanks for the summary David. On a related note, we noticed that there might have been a Tornado Debris Signature (TDS) with the first storm on December 26 at around 1740-1745Z. In examining the data today, I would note that the TDS signal was not a classic one as the reduction in low CC values (some below 0.7) was not associated with a strong rotational velocity couplet (the couplet was much, much stronger on the previous volume scan though). The reflectivity signature was not as clear with Z values of around 45 dBz but ambiguous reflectivity values associated with a TDS is not unheard of. See the 4 panel image linked below.

    I did not see a PNS confirming a tornado. Given the inconsistency in SRM and CC products, it is possible that a brief touchdown occurred near or just after the 1740z scan and the debris was still airborne as the couplet rapidly weakened as indicated in the 1745Z image.

    I had planned on using this event as an example of the TDS and sharing it with staff but I am still uncertain, especially since no tornado was confirmed. But the low CC values make think that some debris from somewhere may have been vaulted into the air.

    I put together a 4 panel image of Z, SRM, ZDR, and CC from 1740 and 145Z on 2012/12/26.
    https://docs.google.com/a/noaa.gov/open?id=0B1K1lG7wfKxMSEk5QWFaTTlqZ2M

    TDS training from the WDTB
    http://www.wdtb.noaa.gov/courses/dualpol/Applications/TDS/player.html

  2. David.Glenn says:

    Thanks for the comments Jonathan. We asked our partners on Camp Lejeune to conduct a fly over of the location and they continued to note no damage. The area that the cell traversed is used for training purposes and contains mostly swampland with a few patches of trees (roughly 34.599N, -77.345W to 34.640N, -77.325W). I forwarded the data and our internal discussion to Paul Schlatter (formerly WDTB) and he agreed that the Tornado Debris Signature (TDS) is present, likely from leaves/pine straw lofted into the air. Paul also asked if the TDS signal was noted at the 0.9 degree level and it is apparent there as well. I’ve added a loop of the 0.5 and 0.9 degree BR, BV, ZDR, and Correlation Coefficient (CC) (RHO in GR2) for the 1731-1750 UTC time frame to the original post. Unfortunately, since we cannot confirm damage through Camp Lejeune, this event will remain non-tornadic.

    I also wanted to address the Dual-Pol data with the confirmed EF1 tornado north of Beaufort. This storm had the TDS signal but it was more apparent at the 0.9 degree level (~1000 feet). The 0.5 degree slice samples at approximately 650 feet and was very noisy due to its close proximity to the radar (~10 nmi). Two new images have been added to the original post which illustrates the reduced CC/local minimum ZDR for 1952 and 1956 UTC. The 0.9 degree Dual-Pol data from the Beaufort tornado represents the more classic case of a TDS and, in my opinion, would be a suitable example for training purposes.

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