It was hitting critters for 660-670, i turned on Sanctity aura (+2% increase to all damage) and it started hitting for 670-680. I popped Avenging Wrath (+30% damage) and it hit for 888 twice, then crit for 1814.
It wasn't raining at this point so doesn't need to be rainding to zap critters.
It works while sat down and while mounted.
[edit] Some further info, when used in a raining zone (Zangermarsh) it was zapping critters for more, hitting around 700-710.
It would not hit mobs if i wasn't in combat, as soon as i entered combat it would start zapping, it would also pull other mobs to me as long as i was in combat.
It seems to have 2 seperate attacks, 1st is the high damage against critters, this can occur out of combat (sitting/mounted) but will not jump to another critter or mob. 2nd is the "normal" damage, this will only occur whilst in combat and can jump to a 2nd target (even if this 2nd mob isn't in combat with you already). This is confirmed by looking at the spell details, it is an aura effect with 2 seperate spell effects.