On 24 August 2016, a tornado outbreak impacted Indiana, Ohio, and Ontario with 26 confirmed tornadoes. Elevated multicellular convection developed into surface-based supercells that produced several tornadoes, particularly near a differential heating boundary. This convective mode transition is of particular interest owing to its relatively rare occurrence. A WRF Model simulation accurately captures the environment and storm evolution during this outbreak. Trajectory analyses indicate that the multicellular updrafts were initially elevated. Since nearly all of the vertical wind shear was confined to the lowest 1 km, significant rotation did not develop via tilting of horizontal vorticity until the storms began ingesting near-surface air. Near-surface vertical wind shear decreased outside of cloud cover owing to vertical mixing, while it was preserved under the anvil, allowing for large values of 0–1-km storm-relative helicity to persist north of a differential heating boundary. Analysis of the perturbation pressure field from the WRF Model output indicates that the development of relatively large nonlinear vertical perturbation pressure gradients coincided with when near-surface air began to enter the updrafts, resulting in upward accelerations in the lowest 2 km, below the level of maximum rotation. In strengthening updrafts, upward-directed buoyancy perturbation pressure accelerations may have offset the downward-directed nonlinear perturbation pressure accelerations above the level of maximum rotation, allowing the updrafts to intensify further.

Despite an increased understanding of environments favorable for tornadic supercells, it is still sometimes unknown why one favorable environment produces many long-tracked tornadic supercells and another seemingly equally-favorable environment produces only short-lived supercells. One relatively unexplored environmental parameter that may differ between such environments is the degree of backing or veering of the midlevel shear vector, especially considering that such variations may not be captured by traditional supercell or tornado forecast parameters. We investigate the impact of the 3-6 km shear vector orientation on simulated supercell evolution by systematically varying it across a suite of idealized simulations. We found that the orientation of the 3-6 km shear vector dictates where precipitation loading is maximized in the storms, and thus alters the storm-relative location of downdrafts and outflow surges. When the shear vector is backed, outflow surges generally occur northwest of an updraft, produce greater convergence beneath the updraft, and do not disrupt inflow, meaning that the storm is more likely to persist and produce more tornado-like vortices (TLVs). When the shear vector is veered, outflow surges generally occur north of an updraft, produce less convergence beneath the updraft, and sometimes undercut it with outflow, causing it to tilt at low levels, sometimes leading to storm dissipation. These storms are shorter lived and thus also produce fewer TLVs. Our simulations indicate that the relative orientation of the 3-6 km shear vector may impact supercell longevity and hence the time period over which tornadoes may form.