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Calcimator

Skew-T Log-P Reader

Estimate atmospheric stability parameters from surface observations and upper-air data. Calculates CAPE, LCL, LFC, and Lifted Index using simplified thermodynamic profiles.

Inputs

°F
°F
mb
°F

Results

CAPE

1,121 J/kg

Stability Category

Extremely Unstable

LCL Pressure876 mb
LFC Pressure832 mb
Equilibrium Level388 mb
Lifted Index-7 °C
Parcel Temp at 500 mb-8 °C
How to Use This Calculator
  1. Enter Surface Temperature (°C), Surface Dewpoint (°C), and Surface Pressure (mb).
  2. Input 500 mb Temperature from a sounding dataset or model output.
  3. Review CAPE (J/kg), LCL Pressure (mb), and LFC Pressure to characterize atmospheric instability.
  4. Check Lifted Index: below -6 = extremely unstable, -3 to -6 = moderately unstable, above 0 = stable.
  5. Use Equilibrium Level and parcel temperatures to estimate storm-top height and convective potential.

How the result changes with Surface Pressure

Surface PressureCAPEStability Category
8251,768 J/kgExtremely Unstable
8881,682 J/kgExtremely Unstable
9631,399 J/kgExtremely Unstable
1,0251,044 J/kgExtremely Unstable

What each input means

Surface Temperature
Observed temperature at the surface station in degrees Celsius.
Surface Dewpoint
Observed dewpoint temperature at the surface in degrees Celsius.
Surface Pressure
Station pressure at the surface in millibars (hPa). Standard sea-level pressure is 1013.25 mb.
500 mb Temperature
Environmental temperature at the 500 mb level (~5,500 m). Obtained from upper-air soundings or model data.

What each result means

CAPE
Convective Available Potential Energy — buoyant energy available for thunderstorm updrafts.
LCL Pressure
Lifting Condensation Level — pressure at which clouds begin to form.
LFC Pressure
Level of Free Convection — pressure where parcel becomes warmer than environment.

How this is calculated

Worked example, using the default values

  1. Identify Input Parameters
    4 parameters
    Surface Temperature = 30, Surface Dewpoint = 20, Surface Pressure = 1013, 500 mb Temperature = -15 = 4 input(s) provided
  2. Calculate CAPE
    CAPE
    1121 = 1121
  3. Calculate Stability Category
    Stability Category
    Extremely Unstable = Extremely Unstable
  4. Calculate LCL Pressure
    LCL Pressure
    876 = 876
  5. Calculate LFC Pressure
    LFC Pressure
    832 = 832

Engine last updated . Checked against 3 independently-derived tests — how we verify calculators.

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