Roar of Thunder is a 13th level cleric Encounter power that was introduced in Heroes of the Fallen Lands.
Roar of Thunder
Cleric Attack 13
Imbuing your weapon with the thundering touch of the god of storms, you unleash divine wrath against your foe.
Melee weapon
Target: One creature
Attack: Wisdom vs. AC
Hit: 3[W] + Wisdom modifier thunder damage.
Effect: The next time you or an ally hits the target before the start of your next turn, the target takes 5 extra thunder damage.