Reposting this since it fell victim to the server move...
Yes, while updraft strength is related to bouyancy (CAPE), it is also strongly affect by storm updraft organization and rotation. For example, given two storms in the same thermodynamic environment -- meaning the same CAPE, the same WBZ level, the same freezing level, etc -- two storms can have signficantly different updraft vertical velocities. A storm with a rotating updraft will have a stronger updraft, despite having available the same CAPE, than another storm without a mesocyclone. Strong vertical wind shear, presumably favoring updraft rotation, induces vertical perturbation pressure gradients, which enhances updraft velocity. So this is a very possible scenario: two storms, same environment -- completely different updraft strengths... Thus the reason why supercells, which have a rotating updraft by definition, produce the vast majority of very large hail, in contrast to the hail produced by other storm modes -- such as squall lines. Heck, a derecho ingesting 6000 CAPE air (the terminology isn't very good, but you understand) can fail to produce hail that a supercell ingesting lesser CAPE can produce (given the same wbz level, freezing level, etc)...
