Effects of Low-Level Vertical Wind Shear Orientation on Low-Level Rotation in Simulated Supercell Thunderstorms

Forecasting which supercells will form tornadoes is no easy task. While great strides have been made in this field over the last decade much remains unknown about tornadogenesis and maintenance. Of all the supercells with radar-detected mesocyclones, only about 25% go on to form tornadoes. With the advancement of numerical models, we have been able to analyze the importance of different environmental parameters that affect supercell tornadoes. Two particularly predictive parameters are the low-level (typically 0-1 km) vertical wind shear and lifting condensation level (LCL).

In this work, idealized soundings are used to simulate supercell thunderstorms using the CM1 model. These idealized soundings are manipulated to change the angle of the 0 – 500 m vertical wind shear vector with respect to the deep-layer hodograph in each simulation. Results from four cases will be presented: the control case, which has no shear in the lowest 500 m, the ‘0 degree' shear case, ‘90 degree' shear case, and ‘180 degree' shear case. These cases will be compared to investigate how the angle of vertical shear orientation affects the developments of low-level rotation in supercell thunderstorms. In particular, it is expected that the sensitivity to the low-level shear is, in part, a product of the outflow position and characteristics in different shear regimes.