A Detailed Analysis of Tornado Events across Northeastern Alabama's Southern Cumberland System

Sand Mountain and Lookout Mountain are two large plateaus that extend along a south-southwest to north-northeast axis from northeast of Birmingham, Alabama, to just southwest of Chattanooga, Tennessee.  These two plateaus, separated by the Wills Valley, form a substantial portion of the southern end of the Cumberland Plateau system, which extends north-northeastward across East Tennessee and eastern Kentucky.  The two plateaus plus the Wills Valley, together hereafter referred to as the Southern Cumberland System (SCS), are located within a tornado-prone region of northeastern Alabama.  Past work has shown repeated observations of parent circulations, both supercellular and non-supercellular, forming or intensifying as storms move over the SCS, particularly Sand Mountain, often quickly followed by tornadogenesis.  Likewise, as storms move off either the Sand Mountain or Lookout Mountain plateau, dissipation of tornadoes and weakening or dissipation of parent circulations is often observed, including when storms remain on the SCS but transition from Sand Mountain to the Wills Valley.  Although these behaviors are believed to be storm-scale influences from the underlying terrain, the exact physical processes through which the terrain may influence storm evolution are not understood.  To further complicate matters, a number of cases exist in which tornadoes formed in the Wills Valley, some of which ascended Lookout Mountain, and cases exist in which strong parent circulations with tornadoes in progress reach the SCS, sometimes leading to disruption of the storms and/or weakening or dissipation of the associated tornadoes.

This presentation serves to further define and quantify tornado events in the SCS region from a myriad of different angles.  This analysis will include, but not be limited to,

1)     Quantifying the occurrence of SCS events, stratified by factors such as tornadogenesis locations for tornadoes that impact the SCS (Sand Mountain, Lookout Mountain, the Wills Valley, or outside the SCS), parent storm mode, time of year, time of day, intensity, and other metrics;

2)     Documenting environmental parameters for SCS events;

3)     Analyzing parent storm evolution as storms propagate from outside the SCS to within the SCS region;

4)     Comparing individual parent storms that impact the SCS to those that do not impact the SCS but occur within the same event; and

5)     Comparing events that produced tornadoes that impacted the SCS to those that did not but rather impacted areas within the vicinity of the SCS.

These preliminary results will be placed in the context of the Verifications of the Origins of Rotation in Tornadoes Experiment – Southeast (VORTEX-SE) field campaign, including narrowing of physical hypotheses and refinement of potential experimental designs for studying both flows atop and around the SCS and storm interactions with the SCS from both observational and numerical simulation platforms.  In addition, these results will aim to assist in the forecasting for VORTEX-SE year-2 operations in the SCS region.