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