Significant Tornado Parameter STP Calculator

Explicit effective-layer CIN-bearing STP normalization1500/150/20 with shear 12.5cutoff/cap 1.5, LCL1000–2000 and CIN−50..−200factors; not fixed-layer variant or forecast. Caller independently establishes matching units, evidence, method edition and applicability; output is not compliance, diagnosis, work-safety approval, geological identity or validated hazard prediction.

Description

The significant tornado parameter combines instability, rotation, shear, cloud-base height and inhibition into a dimensionless environmental index.

The significant tornado parameter combines instability, rotation, shear, cloud-base height and inhibition into a dimensionless environmental index.^{[1, 2]}

Its individual factors represent a particular effective-layer formulation rather than a probability of tornado occurrence. CAPE describes available convective energy, CIN describes inhibition, and LCL is the lifting condensation level. The supplied values must use the mixed-layer and effective-layer definitions expected by this formulation.

When to use Significant Tornado Parameter STP Calculator

Use this tool to calculate or review the supplied observations under the stated rules. Establish the observation method, units, averaging period and applicable reference or calibration.

How to use Significant Tornado Parameter STP Calculator and understand its results

Establish the observation method, units, averaging period and applicable reference or calibration.
Enter mixedLayerCapeJKg, effectiveHelicityM2S2, effectiveBulkShearMS, mixedLayerLclM, signedMixedLayerCinJKg, using the field meanings and rules below, then run the tool.
Read effectiveStpCin, using the output meanings and calculation rules below.
Correct any reported input issue and run again. Before using a successful result, check the stated units, signs, reference scope and observation coverage.

Input field	Meaning	Value type	Requirement
mixedLayerCapeJKg	Mixed-layer convective available potential energy (CAPE), J/kg; nonnegative	number	Required
effectiveHelicityM2S2	Effective-layer storm-relative helicity, m²/s²; nonnegative	number	Required
effectiveBulkShearMS	Effective-layer bulk shear, m/s; nonnegative	number	Required
mixedLayerLclM	Mixed-layer lifting condensation level (LCL) height, metres; nonnegative	number	Required
signedMixedLayerCinJKg	Signed mixed-layer convective inhibition (CIN), J/kg; zero or negative	number	Required

Require nonnegative CAPE, helicity, shear and LCL height, and nonpositive signed CIN. Normalize CAPE by 1500 and helicity by 150. The shear factor is zero below 12.5 m/s and otherwise min(shear/20,1.5); the LCL factor is clamped (2000−LCL)/1000; the CIN factor is clamped (200+CIN)/150. Multiply all five factors. Clamps are inclusive at zero and one.

STP=(CAPE/1500)(helicity/150)×shearFactor×clamp((2000−LCL)/1000,0,1)×clamp((200+CIN)/150,0,1)

Use the matching field units and the exact boundary, ordering and reference rules above.

Output field	Meaning	Value type
effectiveStpCin	Dimensionless effective-layer STP with CIN factor; not a probability	number

json

{
  "input": {
    "mixedLayerCapeJKg": 1500,
    "effectiveHelicityM2S2": 150,
    "effectiveBulkShearMS": 20,
    "mixedLayerLclM": 1500,
    "signedMixedLayerCinJKg": -50
  },
  "output": {
    "effectiveStpCin": 0.5
  }
}

Limitations and assumptions

This implementation has no effective-inflow-base input and does not apply a separate elevated-inflow zeroing rule. Establish that the input profile and this branch of the formulation apply. The result is an environmental index, not tornado probability or an official warning.

Missing required fields, unknown fields, wrong types and violated rules return input issues. Numeric values and outputs must be finite.

Alternative or Complementary methods

For a related step, use DCAPE Downdraft CAPE Calculator: Downdraft CAPE represents integrated favorable downdraft buoyancy along an independently supplied parcel profile. For a complementary comparison, use Low Level Wind Shear Alert Threshold Checker: An along-runway wind change has a sign, while a magnitude threshold screens changes in either direction.

References

Significant Tornado Parameter STP Calculator — tool.io
Effective-layer significant tornado parameter — NOAA Storm Prediction Center

Similar or alternative tools

DCAPE Downdraft CAPE Calculator
Downdraft CAPE represents integrated favorable downdraft buoyancy along an independently supplied parcel profile.
Low Level Wind Shear Alert Threshold Checker
An along-runway wind change has a sign, while a magnitude threshold screens changes in either direction.