Hi there,

Reading into the wording of the Channel Divinity, would a Tempest Cleric be able to wait until target's make their saving throw before activating it?

For example, if one were to cast Shatter, could they wait to see how many targeted enemies succeed their saving throw before deciding to Channel Divinity, or would they have to do so before the saving throws are made?

No. You declare your intentions when you take the action, then you find out how successful you were. 

Actually I think this could be allowed, though I'd say it's ultimately a DM call.

If you look at the Destructive Wrath feature:

When you roll lightning or thunder damage, you can use your Channel Divinity to deal maximum damage, instead of rolling.

So you don't have to trigger this until you actually roll for the damage. So now let's take a look at Thunderwave:

A wave of thunderous force sweeps out from you. Each creature in a 15-foot cube originating from you must make a Constitution saving throw. On a failed save, a creature takes 2d8 thunder damage and is pushed 10 feet away from you. On a successful save, the creature takes half as much damage and isn't pushed.

The first step of resolving the spell is for the target(s) to make their Constitution saving throw(s), you're not told to roll damage until after this has happened. I'd say you have an argument in RAW that you don't have to decide until just before you actually roll the damage (must be before rolling, as you can't roll then decide).

The real question is whether you as the player/cleric have any way of knowing how many enemies failed their saves at this point; this is going to depend upon your DM but strictly speaking they should not tell you how many enemies failed their saves. The only indication you should normally have that a save was failed is when an enemy is pushed 10 feet backwards, but that happens after an enemy takes the damage, so it's too late for you to use to decide when to use this ability.

TL;DR:

You can choose to use Destructive Wrath after the saving throws are rolled, but you're not supposed to know how many enemies failed at that point, so it's of no real benefit to you to do this. You want to look closely at the wording of each spell you take though, as there may be some that give an indication of a failed save before you roll your damage, but iirc I don't think there are any. 😉

Shatter says:

"... Each creature in a 10-foot-radius sphere centered on that point must make a Constitution saving throw. A creature takes 3d8 thunder damage on a failed save, or half as much damage on a successful one. ..."

The saving throw is first and the roll for damage second. edit: but with the damage being the only potential indicator RAW as to whether the saving throw has been successful or not.

Channel Divinity: Destructive Wrath says:

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.

Quote from Brokarian >>

... if one were to cast Shatter, could they wait to see how many targeted enemies succeed their saving throw before deciding to Channel Divinity, or would they have to do so before the saving throws are made?

 
A literal reading would say yes.

The order of operation suggest a spell's damage roll comes after saving throw.

The problem isn't really whether you can roll after the saves (you can with every spell I've looked at); the problem is whether you know how many succeeded before you roll, which RAW you don't but it depends upon your DM.

With Thunderwave there is an indicator of success/failure because an enemy will be pushed 10 feet if they fail, but this happens at the same time as, or after, the damage roll so you can't use this to decide whether to use Destructive Wrath or not. The only way you know how many enemies succeeded/failed is if your DM announces it before you roll the damage, but they're under no obligation to do so (and aren't really supposed to, though it's not uncommon). Spells like Shatter however have no explicit indication of success/failure.

Plus it's actually faster to resolve if the DM rolls the saves while you're rolling damage, so really for convenience you should just decide whether to maximise the damage when you're casting the spell.

But like I say, it depends on your DM; if they announce enemy save results then you can definitely punish them for doing so by choosing to maximise the damage only afterwards, but you might just encourage them to stop doing it 😝

Really though it only matters how many save if you're planning to maximise a cantrip (like Thunderclap) or some other save-or-suck (can't think of any offhand). For spells that still do half damage on a success you're still maximising that damage, so compared to an average roll you'll still be doing double the damage you would have done if you didn't use Destructive Wrath.

It's necessary metagame info to know the outcome of your attacks or spells, wether AC hit/miss or saving throw success/failure.

Quote from Plaguescarred >>

It's necessary metagame info to know the outcome of your attacks or spells, wether AC hit/miss or saving throw success/failure.

You can know that you've hit because that happens, but whether or not you know if an enemy saved depends entirely on the spell/ability.

For example, a DM does not need to reveal whether Charm Person worked unless you act in some way to test it (e.g- speak to the target), otherwise your first indication that they still hate you will be when they continue trying to hack you to pieces during their own turn. This differs for example from Zone of Truth which explicitly states "You know whether each creature succeeds or fails on its saving throw", or a spell like Scrying where something doesn't happen at all if they saved.

Again, it's up to the DM, but they are under absolutely no obligation to tell you anything that your character would not know or be able to observe somehow.

I was specifically talking in the context of a lightning or thunder spell that may  have noticeable effect. There are spells that it is not the case of course.

Don't go full Tempest Cleric.  Be an arcane spellcaster with a two-level dip in Tempest Cleric.  As an arcane spellcaster, you have access to spells like lightning bolt and chain lightning, that can benefit from maximum damage way more than call lightning or destructive wave.  A quick burst of damage makes better use of this ability, because Destructive Wrath only activates once per use.  As a result, you won't be able to get much mileage of this ability out of call lightning, as it takes a slow-and-steady approach to damage.  This multiclass combo is even better if you are a sorcerer with Transmuted Spell.  Then you can transmute cone of cold, fireball, otiluke's freezing sphere, and eventually meteor swarm to thunder damage, dealing maximum damage and also gaining the additional benefit of a superior damage type (fire/cold to thunder).  Wait, the damage stackup is not over yet.  Become a Draconic Bloodline or Storm Sorcerer to add a static bonus to lightning or thunder damage.  Now go destroy the world your DM worked hard to create!  ;D.  BOOM!  CRACK!  

The Tempest CD is really good. But unfortunately the cleric has not much sources of lightning damage to make this shine. So multiclassing is probably the best way for you. In that case you want to take just 2 levels of Tempest Cleric and then turn to sorcerer or druid (Circle of mountain works well).

But what to do, when you want to play a cleric as a main class? When your DM allows it, then you could homebrew and get Lightning Bolt as a domain spell. Just switch out another domain spell of Lvl 3 or higher, that is also not on the standard clerics spell list (e.g. Ice storm out and lightning bolt in). I would allow it until it fits to the theme of the (sub)class. Subclasses are made to bring some flavour to the table and have some fun. And sometimes blasting with full damage is really fun. But the cleric is more than just blasting, keep that in mind!

If I were to use DW on a casting of chain lightning does it apply to All the individual bolts from the casting of the spell, or just the initial bolt? I can see an argument for both options but wondering what the general consensus is here

thanks!

Quote from Saltlick1973 >>

If I were to use DW on a casting of chain lightning does it apply to All the individual bolts from the casting of the spell, or just the initial bolt? I can see an argument for both options but wondering what the general consensus is here

It depends how your DM wants to resolve it I guess; due to the way it's worded it's pretty similar to an area effect spell (every target rolls a save then takes full or half damage) so it'd be reasonable to run it in the same way by rolling once for damage and applying it to every target.

In that case you could argue that Destructive Wrath is operating on a single damage roll, therefore it does maximum damage to every target, and this would be fine in RAW.

Of course, it's also vague enough that you could argue you should roll for each target separately; this would be more consistent with how the spell is described (hits one before hitting the others). In that case you'd only maximise the initial target, and the others would take normal damage.

That seems to make it a DM's decision; a potential maximum of 240 points of damage across four targets is pretty high (and scales fast if you throw a 7th or higher slot at it), but not unreasonable for a 6th level spell since it needs enough targets. Personally I'm leaning towards first target only gets maximised but that's purely my own preference, and I've no strong case for it (and will probably change my mind).

"you can use your Channel Divinity to deal maximum damage, INSTEAD OF ROLLING."

That means at the point you would roll the dice, you instead declare max damage.  Saving throw are rolled after this and then applied.

There is no time limit specified for the Destructive Wave. So couldn't you do max damage to a call lightning for the full spell length?

Quote from Marusk >>

There is no time limit specified for the Destructive Wave. So couldn't you do max damage to a call lightning for the full spell length?

Destructive Wrath is triggered "when you roll lightning or thunder damage", which is when you use your Channel Divinity to maximise that roll (and only that roll); you can only use it multiple times for a single spell if you spend multiple uses of Channel Divinity to do so.