Target: each creature within this power's area of effect
Attack: Intelligence vs. Fortitude
Hit: "4d8 + Intelligence modifier cold damage, and the target is immobilized (save ends)."
Miss: "Half damage, and the target is slowed (save ends)."
Effect: "The burst creates a zone of difficult terrain that lasts until the end of the encounter."[PH:168][Dr401:74]
Greater ice storm is a daily power available to wizards at 29th level. This is a powerful ice spell. Much like meteor swarm, it blasts foes with an large area of effect storm of ice shards.
The "Class Compendium: The Arcanist" article in Dragon 401 added the evocation keyword to greater ice storm.