CAPE — Convective Available Potential Energy
Also: CAPE
At a glance
CAPE is how much fuel a rising parcel of air has in the tank. More CAPE means stronger updrafts and, all else equal, more violent storms.
Deep dive
CAPE is the vertically integrated buoyancy of a lifted parcel between the Level of Free Convection (LFC) and the Equilibrium Level (EL), expressed in J/kg. It's the area on a skew-T where the parcel path is warmer than the environment.
Rough thresholds used in UK forecasting:
- 0–500 J/kg — weak instability, showers or garden-variety thunder.
- 500–1500 J/kg — moderate; organised storms possible if shear is present.
- 1500–2500 J/kg — strong; UK red-flag day.
- >2500 J/kg — extreme for our latitude; check for plume-event signatures.
CAPE alone doesn't make a severe storm. Pair it with shear (see bulk-shear and srh) and consider CIN — a capped environment might store all that energy and never release it.
Most-unstable (MUCAPE), surface-based (SBCAPE), and mixed-layer (MLCAPE) variants exist — UK forecasters lean on MUCAPE because a maritime boundary layer is often cooled and won't initiate, even if parcels a few hundred metres up can.