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Calcimator

Tornado Risk Calculator

Calculate the Significant Tornado Parameter (STP) and Supercell Composite Parameter from CAPE, wind shear, storm-relative helicity, and LCL height.

Inputs

J/kg
knots
m²/s²
m AGL

Results

Significant Tornado Parameter

1.83

Tornado Risk Level

Moderate — Significant tornadoes possible

Potential EF ScaleEF1-EF3 possible
Supercell Composite1.83
Supercell PotentialModerate — Supercells possible
How to Use This Calculator
  1. Enter CAPE (J/kg) from a sounding or model — higher values indicate greater instability.
  2. Set 0-6 km Bulk Shear (knots) — the vector wind difference between surface and 6 km altitude.
  3. Enter Storm-Relative Helicity (m²/s²) and LCL Height (m) from sounding data.
  4. Review Significant Tornado Parameter (STP): values above 1 indicate elevated tornado risk.
  5. Check Tornado Risk Level, Potential EF Scale, and Supercell Potential for complete storm hazard assessment.

How the result changes with CAPE

CAPESignificant Tornado ParameterTornado Risk Level
6000.55Slight — Weak tornadoes possible
2,1001.92Moderate — Significant tornadoes possible
3,9003.57Moderate — Significant tornadoes possible
5,4004.94High — Strong tornadoes possible

What each input means

CAPE
Convective Available Potential Energy in J/kg. Values >1500 J/kg are considered favorable for significant tornadoes.
0-6 km Bulk Shear
Wind shear magnitude over the 0-6 km layer in knots. Values >40 kt support supercell development.
Storm-Relative Helicity
0-3 km storm-relative helicity. Measures rotational potential. Values >150 m²/s² favor mesocyclones.
LCL Height
Lifting Condensation Level height above ground in meters. Lower LCL (<1000 m) favors tornado formation.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    CAPE = 2000, 0-6 km Bulk Shear = 40, Storm-Relative Helicity = 200, LCL Height = 800 = 4 input(s) provided
  2. Calculate Significant Tornado Parameter
    Significant Tornado Parameter
    1.83 = 1.83
  3. Calculate Tornado Risk Level
    Tornado Risk Level
    Moderate — Significant tornadoes possible = Moderate — Significant tornadoes possible
  4. Calculate Potential EF Scale
    Potential EF Scale
    EF1-EF3 possible = EF1-EF3 possible
  5. Calculate Supercell Composite
    Supercell Composite
    1.83 = 1.83

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