312 Observations and Operational Application of the 23 Nov. 2014 QLCS Tornadic Event: Persistent Regeneration of Weak Tornadoes with Pronounced Tornado Debris Signatures

Monday, 11 January 2016
Adam Baker, NOAA/NWSFO, Peachtree City, GA; and J. T. Deese, S. E. Nelson, and G. Lackmann

Handout (2.2 MB)

The tornadic development across central Georgia on the afternoon of 23 Nov. 2014 was not the typical case one would expect in the Southeast U.S. for two reasons, a persistent northern bowing segment or “broken-S” QLCS convective mode resulting six separate tornadoes and pronounced tornadic debris signatures (TDS) seen with five of the six tornadoes, some of which lofted debris to a significant height above the ground more than previously documented with weak tornadoes (Banghoff and Nelson, 2014).

The synoptic setup consisted of a negatively titled upper shortwave trough tracking northeastward across the southeast CONUS with an attendant surface low pressure system advecting moisture off the northern Gulf of Mexico. A parent surface high pressure system situated off the mid-Atlantic coast had previously resulted in hybrid cold-air damming (CAD) along the eastern slopes of the Appalachians, and allowed for the periphery of the wedge of cold air or “wedge front” to be present across central Georgia. The combination of these influencing features provided a high shear low CAPE (HSLC) environment for convective development. Tornadogenesis was observed to consistently occur along the wedge front as it rapidly retreated northeastward across central Georgia ahead of the aforementioned system. It is proposed that this feature provided the nearly steady source of low level streamwise vorticity available for tilting into the vertical within the convective updraft as subsequent downdrafts instigated persistent tornadogenesis by bringing vorticity to the surface. Presence of the front thus compensated for the lack of surface based instability in the HSLC environment and helped focus tornadic development. This serves as an extension to previous research on the influence of the wedge front in conversely low shear high CAPE environments.

Dual-polarization radar data was analyzed during the event in real-time to assist in enhanced wording of the tornado warnings. Trends in the reflectivity, velocity, ZDR and correlation coefficient indicated TDS heights of up to 12 kft (likely debris from a previous tornado which was lifted to higher levels well after the tornado lifted). This height does fit within a common range of 6-20 kft observed with previous research on significant tornadoes in the EF2-EF3 categories (Entremont and Lamb, 2013). While the surveyed tornadoes in this event mainly fit in the weak EF0-EF1 damage categories, it is proposed that the presence of abundant fall foliage and lofted leaf debris may have allowed for such high TDS heights, though previous research included several tornadoes with a TDS during the Fall season in areas with abundant foliage.

The analyzed trends in observed radar data and the associated near-storm environment from this particular case provide unique utility in operations. The findings not only extend the proposed effect of wedge front influence on convection in HSLC environments, but also present an upper bound of TDS height correlation to tornado strength during the fall season. This provides great aid to awareness and enhanced wording in warning decisions.

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