http://www.drjack.info/BLIP/INFO/par...ails.html#CAPE

CAPE
Convective Available Potential Energy is a measure of the
atmospheric stability affecting deep convective cloud formation above
the BL. Higher values indicates greater potential for strong
thunderstorm development and larger updraft velocities. Thunderstorm
strengths associated with CAPE values (as published by Wright-
Patterson AFB) a 0=none, 300-1000=weak, 1000-2500=moderate,
2500-5300=strong [note that these values are relative to the very
large thunderstorms which occur in the Mid-West!]. This parameter
only indicates the potential for thunderstorm formation - for
thunderstorms to actually form also requires some triggering mechanism
which produces upward motion, such as flow over a ridge or
convergence. This parameter is obtained directly from model output
and not from a BLIPMAP computation.