Volatility of Tornadogenesis: An Ensemble of Nontornadic and Tornadic Supercells in VORTEX2 Environments

It is still unclear how differences in the environmental profiles of temperature, humidity, and winds, especially the lower tropospheric wind profile, affect the in-storm processes that lead to tornadogenesis. Observations of supercells have shown remarkable resemblance between nontornadic and tornadic supercells. Despite these similarities, the majority of supercells (at least 75%) do not produce tornadoes. Unfortunately, we cannot yet explain what separates the ostensibly similar nontornadic supercells from tornadic supercells. Recent research has suggested that the orientation of near-surface horizontal vorticity in the inflow environment is determinative of the storm’s tornadic potential due to contrasting low-level mesocyclone configurations. Further questions remain, including the complication that nontornadic and tornadic supercells can coexist side-by-side in nature. What are the range of outcomes in similar storms and environments? Is tornado formation strongly linked to the environment or primarily a stochastic internal process?

These are important operational forecasting issues that are not easily addressed with single-sounding model studies. To tackle these questions, we’ve run an ensemble of high-resolution [O(100 m)] supercell simulations based on the nontornadic and tornadic composite environments from the second Verification of the Origins of Rotation Experiment (VORTEX2). Preliminary results show that although the environment is strongly determinative of the storm’s eventual tornadic potential, some nontornadic storms are occasionally bumped into the tornadic regime.