BL-8 km Vertical Shear Vector (kts)

The Boundary Layer through 8 km above ground level shear vector denotes the change in wind throughout this height. Thunderstorms tend to become more organized and persistent as vertical shear increases. Bunkers et al. 2006 found that long-lived supercells occur in environments with much stronger 0-8-km bulk wind shear ( > 50 kt) than that observed with short-lived supercells.

reference:
Bunkers, M.J., J.S. Johnson, L.J. Czepyha, J.M. Grzywacz, B.A. Klimowski and M.R. Hjelmfelt, 2006: An observational examination of long-lived supercells. Part II: environmental conditions and forecasting. Wea. Forecasting, 21, 689-714.