CAPE (Convective Available Potential Energy) is the amount of energy available to an ascending air parcel. It represents the positive area on a skew-T diagram between the parcel temperature and the environmental temperature. Values are in Joules per kilogram (J/kg).

What CAPE values indicate severe weather?

Generally: 0–1000 J/kg = weak instability; 1000–2500 J/kg = moderate instability with thunderstorm potential; 2500–3500 J/kg = large instability, severe thunderstorm potential; above 3500 J/kg = extreme instability, significant tornado/severe weather risk.

How does this calculator estimate CAPE?

This simplified calculator assumes the surface parcel is already saturated and lifts it moist-adiabatically through the sounding. Positive parcel buoyancy contributes to CAPE, integrated layer by layer. For operational forecasting, use a full sounding package that accepts dew point and computes the LCL.

What is the difference between surface CAPE and most unstable CAPE?

Surface CAPE lifts a parcel from the surface. Most Unstable CAPE (MUCAPE) lifts the parcel with the highest equivalent potential temperature (usually from the lowest 300 hPa), which gives the maximum possible CAPE. This calculator computes surface CAPE.

Why are pressure levels needed?

CAPE is integrated over height (or equivalently pressure). Pressure levels let the tool calculate layer thickness using the hypsometric equation, which converts pressure differences to approximate height differences needed for the energy integral.

Convective Available Energy

Enter surface and upper-atmosphere temperature and pressure data to calculate CAPE and assess thunderstorm and severe weather potential.

Sounding Inputs

Surface Parcel Temperature (°C)

Temperature of the air parcel at the surface.

Surface Pressure (hPa)

Atmospheric Sounding Levels

Enter at least 2 levels (pressure in hPa, temperature in °C). Levels are automatically sorted top-down.

Enter sounding data and click Calculate CAPE.

CAPE Value

J/kg

Stable

Instability Scale

01000200030004000+

Stable Weak Moderate Large Extreme

Level Breakdown

Pressure (hPa)	Env. Temp (°C)	Parcel Temp (°C)	Buoyancy

Interpretation

Summary

Enter surface and upper-atmosphere temperature and pressure data to calculate CAPE and assess thunderstorm and severe weather potential.

How it works

Enter the surface parcel temperature (the temperature of the air near the ground that will lift).
Add at least two atmospheric levels, each with a pressure (hPa) and the environmental temperature at that level.
The simplified model assumes a saturated surface parcel and lifts it moist-adiabatically through the sounding.
At each level where the parcel is warmer than the environment, positive buoyancy contributes to CAPE.
CAPE is numerically integrated over all buoyant layers and displayed in J/kg with a severity rating.

Use cases

Assess thunderstorm and severe weather potential from radiosonde sounding data.
Understand atmospheric instability concepts in meteorology coursework.
Estimate CAPE from simplified two-level sounding profiles for field forecasting.
Compare instability between different atmospheric soundings.
Learn how parcel theory underlies convective forecasting.
Evaluate whether conditions support ordinary thunderstorms vs. supercells.

Frequently Asked Questions

Last updated: 2026-09-22 · Reviewed by Nham Vu