CAPE Atmospheric Instability Calculator
Estimate CAPE (Convective Available Potential Energy) and Lifted Index from surface temperature, dewpoint, and 500 hPa temperature to assess thunderstorm potential.
CAPE — Convective Available Potential Energy Measures the energy available for a rising air parcel — the fuel for thunderstorms. Higher CAPE means greater storm intensity potential.
CAPE Classification (J/kg)
- 0–300: Weak — thunderstorms unlikely
- 300–1,000: Moderate — ordinary thunderstorms possible
- 1,000–2,500: Large — severe thunderstorms likely
- 2,500–3,500: Very large — violent storms likely
-
3,500: Extreme — extreme severe weather
Lifted Index (LI) LI = T_environment_500hPa - T_parcel_500hPa Negative LI means the parcel is warmer than the environment — it rises freely.
- LI > 0: Stable
- 0 to -2: Marginally unstable
- -2 to -6: Moderately unstable
- < -6: Extremely unstable
Lifted Condensation Level (LCL) The altitude where a surface air parcel cools to its dew point and forms clouds. LCL height ≈ 125 × (T_surface - T_dewpoint) metres
Parcel Temperature at 500 hPa The calculator uses standard adiabatic lapse rates:
- Dry adiabatic lapse rate: 9.8°C/km (below LCL)
- Moist adiabatic lapse rate: ~6°C/km (above LCL, while condensing) 500 hPa is approximately 5,500 m altitude (varies with temperature).