Investigating the Environment of the Indiana and Ohio Tornado Outbreak of 24 August 2016 Using WRF Model Simulation

On 24 August 2016, a tornado outbreak impacted Indiana and Ohio with 22 confirmed tornadoes. Though thunderstorms were predicted for this area, a tornado outbreak caught many meteorologists by surprise since many morning convection allowing models did not depict either cellular convection or significant updraft helicity across this area. Despite these model forecasts, strong low-level shear, adequate deep-layer shear, low LCLs, and plentiful instability provided an environment favorable for the development of supercells and tornadoes. Of particular interest is the transition of the convection from a linear mode to a cellular mode between 1700 and 1900 UTC, after which time tornadoes began to occur.

Observations depict a mesoscale convective vortex (MCV) approaching Illinois in the early morning hours of 24 August. Visible satellite imagery indicates that deep convection initiated on the eastern flank of this MCV and it is believed that this MCV helped augment the low-level across the affected area. An analysis of WSR-88D data depicts the lack of a strong gust front with this early-day linear convection, which may have helped the convection to transition to a supercellular mode. Previous studies have demonstrated that a cloud-layer shear vector with a component normal to the gust front greater than 8 m s^-1 is desirable for transition from a line to cells. A review of mesoanalysis data suggests that the shear vector became favorable for a transition to a cellular mode between 1700 and 1900 UTC.

The WRF model is used to simulate this event. Preliminary simulations are proving the difficulty of capturing the transition from a linear to a supercellular mode. In the simulations, the line of convection generally persists instead of transitioning to discrete supercells. Model output will be presented and analyzed to investigate the changing environment during this event and possible reasons for the mode transition.