I would prune it as a group 3, hard prune this year and perhaps next year and after that treat it as the group 2, light prune, that it is.

Group 2 means remove dead stems in early spring. Blooms on old wood and doesn't need hard pruning every year.

However, pruning all Clematis hard the first three years gets them off to a better start and it is something you can always do to rejuvenate.

So the hard prune for this year whould be done now, or after it finishes flowering? Do I cut it back to the ground, or 12" from the ground?
thanks!

I would do it now since you are in a cold zone. 12" should be fine.