Tempest cleric seems like a fun idea.

If you could change the damage type on a wand of fireballs I'd with that. It's easier to hit more targets. If not, take the wand of lightning bolts.

If you can change the damage for magic missile, then you'd have guaranteed movement. No save, no to hit roll. Thunderwave and Shatter as lightning become good uses of first and second level spell slots.

You might want to consider 2 levels of evoker for sculpt spells. So Tempest cleric 7, Evoker 2. Then you could sculpt a lightning fireball and push all of the enemies around.

In addition to the wand, I like the uncommon amulet of the devout and then maybe winged boots or a broom of flying.