I could see dropping it to 1 constitution damage though, which would make it rather more comparable with the Wounding weapon ability (though Sandstorm blast would have a save).
Draconic Toughness, the similar invocation in question, is in fact a Greater Invocation, and got a pretty good rating in the Dragonfire Adept guide. Admittedly, I found that a little puzzling, hence my addition.Shield of the Depths i'm not sure about. I'd say it was lesser if you just restored it as a Standard action [like other, similar Invocations]. I'm never sure about fast healing as a feature: it's often barely worth it.
I might have gone a little overboard with it, but I do think it is a good idea to give it a range (it's not as good to be able to make a tornado if you practically wind up inside it), and limiting its effects by season makes it a lot less useful (in autumn, for example... well, it kind loses most of its potential).Sing the Winds seems a little excessive for even a Dark power. If it were a normal Control Weather it would probably be fine. Not that there's all that much you can do with it, in combat at least.
Raising its casting time back up to 10 minutes might not be a bad call though, as well as giving it a more clear range than anything you can see (to prevent tossing a tornado on someone with a scrying spell or some such, for example).
On Water Blast, yeah, probably needs a niftier name. I'm not sold on Hydraulic blast though... I didn't think to put in a clause about putting out fires, because... well, it creates water. Kinda seemed intuitive to me, but then, this is D&D and intuition is not to be relied on.
Heh, thanks. I wanted to make a fire invocation that wasn't just 'it deals damage,' like so many fire effects are, and for some reason I kept thinking of Dancing Lights... and then Ward Torch! I'm pretty pleased with how it turned out as well, but I think my favorite is either Wind Force or Work the Waters.All the rest look fine. I like Ward Torch especially.