I just got Blizzard IV. Is there a practical application for this spell? It's Ice. Ice is meant for replenishing mana. It has been since we got our first fire spell and we learned that we cannot simply keep pressing that button or we'd run out of mana and never get it back.

It does roughly 250 more damage than Blizzard 3, doesn't replenish Umbral Ice, and will interrupt cast if either Umbral Ice or Enochian fall off. This means that you have to do everything exactly right or you lose the ability to cast it. This is easy when facing a combat dummy, but in a progression fight, that kind of focus is next to impossible.

Basically, and back to my original point, Using Blizzard III allows you to keep up full stacks of Umbral Ice and max your mana so that you can go back to using the higher damage fire spells. It takes too long to set things up for Blizzard 4 and that time can be spent moving out of AoE spells that will always land underneath our feet!

Or am I missing something?