Characteristics of Vertical Wind Profiles near Supercells Obtained from the Rapid Update Cycle

Abstract

Over 400 vertical wind profiles in close proximity to nontornadic and tornadic supercell thunderstorms are examined. The profiles were obtained from the Rapid Update Cycle (RUC) model/analysis system. Ground-relative wind speeds throughout the lower and middle troposphere are larger, on average, in tornadic supercell environments than in nontornadic supercell environments. The average vertical profiles of storm-relative wind speed, vertical wind shear, hodograph curvature, crosswise and streamwise vorticity, and storm-relative helicity are generally similar above 1 km in the tornadic and nontornadic supercell environments, with differences that are either not statistically significant or not what most would regard as meteorologically significant. On the other hand, considerable differences are found in these average vertical profiles within 1 km of the ground, with environments associated with significantly tornadic supercells (those producing tornadoes of at least F2 intensity) having substantially larger low-level vertical wind shear, streamwise vorticity, and storm-relative helicity compared to environments associated with nontornadic supercells and weakly tornadic supercells (those producing F0 or F1 tornadoes). These findings may partly explain the extraordinary difficulty in discriminating between tornadic and nontornadic supercell environments in a forecasting setting, given the low temporal and spatial frequency of wind observations in the lowest 1 km. It is believed that it would be a worthwhile investment to augment low-level wind profiling capabilities, in addition to taking a closer look at the dynamical sensitivities of supercell storms to near-surface wind shear by way of high-resolution numerical simulations.