CAPE – Convective Available Potential Energy. A measure of available energy related to the buoyancy of a parcel of air. Positive CAPE means that moist, warm air will rise. It is a measure of the instability of the atmosphere responsible for the formation of thunderstorm and other convective (rising air) precipitation.
Higher CAPE implies higher more available energy and more severe storms are possible.
CAPE can be calculated at the surface or it can be calculated as the integrated sum in different layers. It’s measured in Joules/kilogram of air.
On average, surface CAPE of 1000 J/Kg is usually sufficient for strong to severe storms. CAPE of 3,000 to 4,000 J/Kg or higher is usually a signal of a very volatile atmosphere that could produce severe storms if other environmental parameters are in place.