Estimations of CIN and LFC associated with tornadic and nontornadic supercells

It is generally understood that tornadoes are less likely in environments where surface-based instability is absent and the only convective available potential energy (CAPE) is from elevated parcels originating well above the surface. However, little research has been done to examine tornado occurrence in environments where surface-based CAPE is clearly present, but located above a deep layer of surface-based convective inhibition (CIN) associated with a relatively high level of free convection (LFC) heights. A database of 518 model analysis soundings was collected during 2001-03 from recent versions of the rapid update cycle (RUC) analysis and forecast system. All model sounding profiles were in proximity to selected supercell storms associated primarily with tornado warnings, and were nonelevated with surface-based CAPE present. This database is used to examine CIN and LFC to determine environments where instability from mixed-layer and surface-based parcels was associated with significant negative buoyancy in low levels. Findings evaluated for tornadic and nontornadic supercells show that the frequency of F1-F4 intensity tornadoes decreased significantly for increasing CIN and LFC height. The fact that tornado warnings were issued for many nontornadic supercells with large CIN and high LFC heights in the database examined suggests that better awareness of environments having increased CIN and LFC characteristics may be useful operationally in discriminating between some tornadic and nontornadic supercell settings.