33% chance to proc, and a 5 sec ICD.
So playing around a bit with this in the mists. It seems that on AoE abilities the ICD isn't shared between mobs (credit to Kionius on reddit for starting to look into this). I was able to proc several chill effects from meteor shower within 5s of each other.
Did you see anything like this, or were you able to look into this in a multi target situation at all?