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)/1000 m) * (ESRH/150 m2 s-2) * (EBWD/20 m s-1) * ((200+mlCIN)/150 J kg-1)

The mlLCL term is set to 1.0 when mlLCL < 1000 m, and set to 0.0 when mlLCL > 2000 m; the mlCIN term is set to 1.0 when mlCIN > -50 J kg-1, and set to 0.0 when mlCIN < -200; the EBWD term is capped at a value of 1.5 for EBWD > 30 m s-1, and set to 0.0 when EBWD < 12.5 m s-1. Lastly, the entire index is set to 0.0 when the effective inflow base is above the ground.

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.

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