Total Cape, low-level CAPE, and LFC in significant tornado events with relatively high LCL heights

Lifting condensation level (LCL) height is used widely as a limiting parameter in supercell tornado forecasting based on recent studies confirming that most significant tornadoes are associated with mixed-layer LCL height environments less than 1200-1300 m above ground level (AGL). However, a recent study noted that some supercell tornadoes, particularly those in the high plains of the United States, occur with LCL height environments that are higher (e.g., > 1300 m AGL).

To explore this further, a database of Rapid Update Cycle (RUC) soundings associated with tornadic supercells is used in this study to examine significant (F2+ intensity) tornado cases associated with mixed-layer LCL heights considered “relatively high” (e.g., 1300 to 2000 m AGL) based on recent studies. Of 212 RUC soundings associated with significant tornadoes during 2001-2005, 44 (21%) had mixed-layer LCL heights in this range. In these cases, additional thermodynamic parameters were explored to see if other common characteristics could be found that might help forecasters identify such events.

When wind shear and convective available potential energy (CAPE) are favorable for supporting supercell tornadoes, results suggest that low-level (0-3 km) CAPE and LFC height can offer additional clues to signficant tornado environments where LCL heights appear "relatively high". The presence of low-level CAPE in such settings indicates a strongly surface-based environment with a relatively deep low-level moist layer and the absence of an inhibiting inversion, despite spreads between surface temperature and dewpoint that appear rather large.

These results will be documented and discussed, and some recent “high" LCL supercell tornado events will be examined.