Very basic BLM question

[wereotter]

The only time it could get interrupted is if you move or you lose Umbral Ice, and thus lose Enochian. I doubt you are moving when you are attacking a dummy, so it would mean Umbral Ice is falling off, which means you are casting way too slow as it is really easy to fit the cast for T3 and B4 into the UI timer and have plenty of time spare.

This is what I was thinking.

What's your spell speed? If that stat is too low, it's possible you're losing Umbral Ice before you get to cast Blizzard 4, though that should be unlikely.