**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 m^{2} 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.

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