High-Shear Low-CAPE Supercell Simulations

Nearly half of all tornadoes in the United States occur with MLCAPE less than 1000 J kg^-1, and 16 percent of significant (F/EF2+) tornadoes occur with MLCAPE less than 500 J kg^-1 (Schneider and Dean 2008). Yet tornado watch (Dean and Schneider 2008) and warning (Anderson-Frey et al. 2016) performance is diminished in low-CAPE environments. Furthermore, high-shear low-CAPE (HSLC) events are most common in the Southeast (e.g., Guyer et al. 2006; Schneider et al. 2006; Sherburn and Parker 2014), which has unique geographic vulnerabilities (Ashley 2007). These dangers call for an improved understanding of storm behavior in HSLC environments. Several recent high-resolution modeling experiments have elucidated within-storm structures and processes likely involved in supercell tornadogenesis. However, these experiments have almost exclusively featured moderate- to high-CAPE environments typical of the Great Plains rather than HSLC environments typical of the Southeast. Here, this approach is extended to low-CAPE supercells. Several idealized supercells are simulated with CM1 (Bryan and Fritsch 2002) at 100-m horizontal grid spacing using VORTEX-SE observed profiles and HRRR analysis profiles as base states. Results presented include production of small tornado-like vortices in environments ranging from 300 to over 1000 J kg^-1 CAPE, storm behavior preceding vortexgenesis, comparison of simulated cold pools to observations, and vorticity origins.