Significant Tornado Parameter (effective layer)

A multiple ingredient, composite index that includes effective bulk wind difference (EBWD), effective storm-relative helicity (ESRH), 100-mb mean parcel CAPE (mlCAPE), 100-mb mean parcel CIN (mlCIN), and 100-mb mean parcel LCL height (mlLCL).

The index is formulated as follows:

STP = (mlCAPE/1500 J kg-1) * ((2000-mlLCL)/1500 m) * (ESRH/150 m2 s-2) * (EBWD/20 m s-1) * ((200+mlCIN)/150 J kg-1)

When the mlLCL is less than 1000 m AGL, the mlLCL term is set to one, and when the mlCIN is greater than -50 J kg-1, the mlCIN term is set to one. The EBWD term is capped at a value of 1.5, and set to zero when EBWD is less than 12.5 m s-1. Lastly, when the effective inflow base is above the ground, the entire index is set to zero. A majority of significant tornadoes (F2 or greater damage) have been associated with STP values greater than 1 within an hour of tornado occurrence, while most non-tornadic supercells have been associated with values less than 1 in a large sample of RAP analysis proximity soundings.

Additional information can be found here. (Please open this link in another browser window.)