Rusty, yes the surface pressure tendency is a 3hr value. Multiply it by
10800 seconds and divide by 100 Pa to get mb. You are right about the CAPE
being "best possible parcel" (in the lowest 180 mb), not surfaced based, as well. Right now that
is the only CAPE we're offering, but as always, if there's a demand we could
calculate surface-based.

Thanks for your interest!
Tracy Lorraine Smith (wearing my "Stan" hat today)