D&D 5E Fog Cloud: Time To Dispersion?

[vlysses]

Hi, I would like to understand how you guys are playing the dispersion of a fog cloud once the caster drops concentration.

So as a druid, I cast fog cloud, eg in a room. Room becomes heavily obscured, noone sees anything. Now i'm dropping concentration for the fog cloud as I want to cast another concentration spell.

The fog cloud spell specifically states that it "lasts for the duration", ie. 1 hour, or until a wind disperses it. Now given the lack of wind in an enclosed room, would you say the fog stays there for the next hour, even if I drop concentration, or pof, when i drop concentration, the fog disappears?

Or something in between?

What do you say?

 

[ExploderWizard]

The fog cloud lasts for UP TO 1 hour not 1 hour. That up to is very important because it means if you drop concentration prior to the hour duration, the fog cloud disperses.

 

[vlysses]

yes, well that was my point - i realise that the spell lasts 1 hour, but then, you know, in a closed room, fog does not disperse that quickly... or are we saying given it got there magically, it also disappears magically within one round once i drop concentration?

 

[Jaelommiss]

Regarding spells requiring concentration PHB page 203 states "if you lose concentration, such a spell ends." It's pretty clear that this occurs instantly and not over a duration. We might conclude that Fog Cloud, as a concentration spell, ends when concentration ends.

Next, let's look at how the spell would behave depending on whether or not it instantly vanishes when concentration ends. If it disappears when concentration is broken, then concentration is important to the spell's effect. It introduces ways that the spell can end early. Conversely, if it didn't end when concentration ended, then it would make no difference at all if we removed concentration from the spell. Given that the designers did make it a concentration spell, I would assume that being a concentration spell is supposed to have some impact on its effects.

For an example of a spell that does continue after losing concentration look at Conjure Elemental. It clearly states that "if your concentration is broken, the elemental doesn't disappear (PHB, 225)." Such text is not present in Fog Cloud, and so it seems probable that it is supposed to end if concentration is broken.

For these three reasons I would rule that Fog Cloud ends immediately if concentration is broken.


As an interesting side note, a 10 mph wind clocks in at 3 on the Beaufort Scale (wikipedia link), which corresponds to a "gentle breeze" where "leaves and small twigs [are] constantly moving."

 

[I'm A Banana]

yes, well that was my point - i realise that the spell lasts 1 hour, but then, you know, in a closed room, fog does not disperse that quickly... or are we saying given it got there magically, it also disappears magically within one round once i drop concentration?

When the magic ceases to create it, it disappears. One way to think of it: you're not just calling up a fog cloud once and then walking away. You're continuously calling up and sustaining the fog with your magic for the entire duration. So if you stop concentrating on the spell, you're no longer creating the effect, and the fog goes away immediately.

 

[the Jester]

It's magic. It lasts until you stop concentrating (to a maximum of 1 hour). Then it is over and done. The fog dissipates at the end of the duration.

Spells that last past their duration have a duration of "instantaneous".

 

[vlysses]

ok, many thanks... sounds right what you all are saying :-(
[MENTION=6775925]Jaelommiss[/MENTION]: funny you mention conjure elemental, the idea behind the question was originally to somehow combine fog cloud with an earth elemental and his tremorsense. So EE suffers no penalty in the fog cloud, and basically crushes everything to mush in a room for example... I have to think of another way, probably via an item, that creates fog cloud...

 

[the Jester]

ok, many thanks... sounds right what you all are saying :-(
[MENTION=6775925]Jaelommiss[/MENTION]: funny you mention conjure elemental, the idea behind the question was originally to somehow combine fog cloud with an earth elemental and his tremorsense. So EE suffers no penalty in the fog cloud, and basically crushes everything to mush in a room for example... I have to think of another way, probably via an item, that creates fog cloud...

That's a good tactic! However, bear in mind that most items that cast spells actually let the user cast the spell and still require concentration. The easiest thing is probably to have a buddy cast the fog cloud, since it's low level and on several spell lists.

 

[Ancalagon]

The reason the fog disperses is that the local conditions are not "right" for a fog... otherwise there would be a fog already! Basically it's too dry, and all the little droplets evaporate. There may be visible wisps, thin patches that last a few more rounds after the spell end, but the thick pea-soup like fog portion goes away very quickly.

BTW, have any of you been in such a thick fog in real life? I have, only once. The fog was so thick that if I stretched out my arm and spread my fingers, I had a hard time seeing them. It is *eerie* as heck. I mean in even in a "normal" heavy fog you have a few dozens of feet of visibility at least. It takes exceptional conditions (or magic) to create the thickness described by the spell.

 

[Ancalagon]

I like the Earth Elemental combo.

Another one is to put an obstacle hidden by the fog. It could be as mundane as caltrops or as dangerous as Evard's Black Tentacles - basically the enemy will try to push through the cloud to reach the party and then fall victim to the hidden obstacle.