a 5th Edition D&D Build
by Steve & Matt
Hey folks, this is the first post in a series taking quick looks at different builds, each focused on a specific mechanic or theme. We are going to start off with a very simple idea: doing high amounts of damage within a round. One class specialization that does this with ease? The Tempest Cleric.
Mechanic: Use Channel Divinity to maximize the damage of bolts of lightning created by Call Lightning. Keep Call Lightning going as long as needed to finish off opponents.
Damage type: AoE lightning (burst, sustained)
Strengths: High burst damage, moderate sustained damage potential, limited battlefield control, can use a single spell slot per encounter (spell slot of 3rd Level or higher).
Weaknesses: Not effective against anything immune to lightning damage, not effective indoors, requires concentration, uses up character’s action to inflict damage.
Other Features: Moderate hit dice, heavy armor, limited permaflight.
The beauty of this build is in its simplicity. This is just a class doing what it is meant to do, no rules lawyering or shenanigans. At Level 2, the Tempest Cleric gains Channel Divinity: Destructive Wrath. Remember, this allows the cleric to deal maximum damage with a lightning or thunder spell of ANY level. The compares very favorably with the Evocation Wizard’s Overchannel (which can only affect wizard spells of 5th level or lower) and the Sorcerer’s underwhelming Empowered Spell.
At Level 5, the Tempest Cleric gains Call Lightning as a domain spell. It lasts for up to 10 minutes, which is equivalent to 100 bolts of lightning. Each bolt can hit multiple targets, affecting everything within 5 feet of the point of impact. Because you can increase the bolts’ damage by casting Call Lightning from a higher spell slot, from Level 5 to Level 20 this spell scales extremely well with character level.
By Level 18, you will be able to cast Call Lightning from a 9th Level spell slot and maximize up to 3 of the bolts of lightning. Under normal conditions, that’s 90 damage for each maximized bolt and 9d10 for each normal bolt (on a failed save). In stormy conditions, the damage is increased by 10 and 1d10, respectively. Oh, and you can do all of this while flying, thanks to the Level 17 ability Stormborn. Unfortunately, this only works while outdoors, so you might want to skip out on those scary dungeon dives.
Whether you’re interested in devastating a single opponent or whittling down an army, this is a build worth considering.
Orc Labs 
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This is slightly off: you gain 9th-level spells in 5e at [Caster Level 17]. This means that if you wanted to dungeon-dive, you could very well stick to Shatter (base 3d8, 10d8 at max level) for slightly-less max damage. Or you could even do something insane like multiclass as a (probably Evocation) Wizard for 11 levels, gain “Chain Lightning” (10d8 base, increases number of targets with higher spell slots), keep 6 levels of Tempest Cleric (gaining “Call Lightning” for outside use, ‘Thunderbolt strike’ to push enemies away), and 3 random class levels.
Since this is a very WIS/INT-heavy build, to prevent it from becoming “MAD” I would recommend either Wizard or Cleric (to increase potential spell availability and maximize feat options, something like Wizard 12/Cleric 8 would be best) or perhaps a DEX-based martial class (a couple classes in Rogue or Fighter).
Hope you checked out the Tempest Evoker build that was the follow-up to this post! It is quite similar to what you suggested.
I need to read the wording in 5e RAW, but if it is like the 3.5 Call Lightning + Sudden Maximize combo, ALL of the bolts deal full damage, because they are all from one spell.
The wording of Channel Divinity: Destructive Wrath is:
“Starting at 2nd level, you can use your Channel Divinity to wield the power of the storm with unchecked ferocity. When you roll lightning or thunder damage, you can use your Channel Divinity to deal maximum damage, instead of rolling.”
No ambiguity there. You only get this benefit on one damage roll, not the whole spell.
It says channel divinity is used for damage roll not per spell so your only able to use it once.