Stats are calculated on the same frame that the button press is detected.
On cast triggers happen after the ability object is created, often 1 frame after the button press is detected.
So Avalanche does not benefit from the increased physical and spell damage from the set I linked?
Any physical spell damage done by Avalanche is increased by halvar if you have cast a cold spell recently.
A spell can't trigger a if you cast recently buff for itself.
Edit: if you cast it twice in a row, the first one will buff the second one and that one will buff the next one and so on. But the first one isn't buffed.