Does higher Durancy of Weathermagic augment the dam the spells deal?
It doesn't augment the damage an sich,
but for acid rain and meteor shower the same enemy may be hit several times (which is of course a huge advantage).
For lightning storm and wind of furies however I don't really see an advantage (wind: cone lasts longer, damages enemies that wander into it will be hit if it's still there, for lightning storm I failed to see any advantage whatsoever).
I'm in the catacombs now - and found the last BF-key. But is there a way down somewhere? I'm starting to feel blind...
As I don't know exactly what level you're at...
Maps Act 3