SPELL_FIRESTORM

Usage       : cast firestorm
Accumulative: -
Duration    : Instantaneous
Level       : Level 20 cleric
Damage Type : Fire, Holy
Mana Usage  : 7 mana + 7 mana per victim

With the firestorm prayer, the cleric calls the wrath of his deity down
upon his enemies. If outdoors, this manifests itself as a short-lived
maelstrom of fiery rain. If indoors, great, swirling pillars of flame
will shoot up from the floor and surround each enemy. A saving throw
is allowed for each victim to reduce the damage taken.

The inital amount of mana this spell uses is dependant on the caster
level and gradually decreases as levels increase.