Target: each creature in the area of effect
Attack: Intelligence vs. Fortitude
Hit: "1d8 2d8 + Intelligence modifier cold damage."
Miss: "Half damage."
Effect: "The burst creates a zone that lasts until the end of your next turn or until you dismiss it as a minor action. Any creature that enters the zone or starts its turn there takes 5 cold damage (a creature can take this damage only once per turn). The cloud lasts until the end of your next turn. Any creature that enters the cloud or starts its turn here is subject to another attack. You can dismiss the cloud as a minor action."[PH:160]
Sustain minor: "The zone persists until the end of your next turn."[Dr401:55][U :12/2011]
Freezing cloud is a daily power available to wizards at 1st level.
The "Class Compendium: The Arcanist" article in Dragon 401 added the evocation and zone keywords to freezing cloud, increased its initial damage, modified the effect of the zone it creates, and allowed the zone to be sustained as a minor action. The December 2011 update finalized these changes.