Wind blast readied vs casting a spell

Question

The concentration rules give several situations that require a concentration check but supernatural abilities and most combat maneuvers are not among them.

If someone with the wind subdomain readies an action to use his wind blast if an enemy in range tries to cast a spell, does the caster have to make a concentration check? And if so what is the DC.

It is not a spell, so the caster is not affected by a spell. It deals no damage, doesn't grapple or entngle. It may move the caster if successful so is it violent or vigorous motion? Or maybe violent weather?

Does Wind Blast used with a ready action have a chance to interrupt a spell?

Answer 1

While the supernatural ability wind blast is not a spell, this GM thinks it safe to treat the ability as one if the wind blast's user takes the ready action and picks the action use wind blast and the trigger when that dude starts casting.

In fact, this GM tends to read the section on Spells (see below) broadly, allowing any extraordinary, spell-like, or supernatural ability to be used in a manner similar to spells to distract casters. On Magic on Concentration on Spells says

if you are affected by a spell while attempting to cast a spell of your own, you must make a concentration check or lose the spell you are casting. If the spell affecting you deals damage, the DC is 10 + the damage taken + the level of the spell you’re casting.

If the spell interferes with you or distracts you in some other way, the DC is the spell’s saving throw DC + the level of the spell you’re casting. For a spell with no saving throw, it’s the DC that the spell’s saving throw would have if a save were allowed (10 + spell level + caster’s ability score).

(Emphasis mine.) Certainly, a raging blast of wind is capable of distracting the caster! As the supernatural ability wind blast is unique therefore not possessing a spell level and since it was acquired at level 1, this GM would, for the purposes of distracting casters, consider the supernatural ability wind blast the equivalent of a 1st-level spell, but ask your GM.

All in all, it's pretty safe to read that Spells section as Special Abilities and Spells rather than as Spells alone. It doesn't make sense¹ that a wizard could cast normally while affected by the supernatural ability wind blast yet must make concentration checks if affected by the spell gust of wind.

That said, this GM would have the caster make a concentration check (DC 11 + the user's ability score) to avoid losing the spell due to the supernatural ability wind blast as the effect typically doesn't allow a saving throw.

"Why not just use the concentration check DCs for something other than spells when using wind blast?"

In the case of concentration checks, the game seems to care more about an effect's source than an effect's result. That is, were a caster interrupted by the spell gust of wind, then the caster makes a concentration check against that spell's DC and not against, for instance, the concentration check against "wind-driven hail, dust, or debris" (which is also lower than the DC for a spell at DC is 10 + level of the spell the caster's casting).

And while violent motion includes "being pitched roughly" as if one were "on a galloping horse, taking a very rough ride in a wagon, on a small boat in rapids or in a storm, on deck in a storm-tossed ship," the caster still makes a concentration check instead against a spell's DC if affected by a spell even if the spell's result resembles one of those effects.

Basing the concentration check for special abilities other than spells on results rather than effects means the GM evaluates each effect and categorizes them himself arbitrarily, which this GM can see having unintended consequences like overpowered but low-level effects, underpowered high-level effects, and unhappy players.

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¹ I don't typically use the It doesn't make sense argument because usually, to somebody, it does make sense. I'm not sure who that individual would be in this case, but I look forward to that answer.

Answer 2

Treat the wind blast as a bull rush attempt

Wind Blast says:

Wind Blast (Su): As a standard action, you can unleash a blast of air in a 30-foot line. Make a combat maneuver check against each creature in the line, using your caster level as your base attack bonus and your Wisdom modifier in place of your Strength modifier. Treat the results as a bull rush attempt.

A bull rush is a combat maneuver that does not cause harm, but will move the target against their will around the combat zone.

On the concentration rules, we have a few options that are not based on spells and do not calculate the concentration DC based on the spell levels, but that can be used for being moved around against your will, such as:

Violent Motion: If you are on a galloping horse, taking a very rough ride in a wagon, on a small boat in rapids or in a storm, on deck in a storm-tossed ship, or being pitched roughly about in a similar fashion, you must make a concentration check (DC 15 + the level of the spell you're casting) or lose the spell. If the motion is extremely violent, such as that caused by an earthquake, the DC is equal to 20 + the level of the spell you're casting.

What we need to quantify now is the strenght of that motion, is it similar to an earthquake or weaker than that? We can look up the rules for earthquakes and see if we find anything about that:

Volcanic Tremor (Hills, Mountains) Though active volcanoes are rare, even dormant volcanoes can produce tremors. Tremors last anywhere from 1d4 rounds to 2d6 minutes and increase Climb DCs by 2. The tremors might start an avalanche or collapse a cave or cliff (similar to an earthquake spell).

Well, that does sound strong, but let's look at the spell Earthquake then:

When you cast earthquake, an intense but highly localized tremor rips the ground. The powerful shockwave created by this spell knocks creatures down, collapses structures, opens cracks in the ground, and more.

Nope, that's not it, a bull rush cannot knock a creature down, nor open cracks or collapse structures, so a Windgust is definitely weaker than an earthquake.

So, to calculate the concentration check DC, we can do:

• DC 15 + the level of the spell you're casting.

A wind blast is like a telekinetic bull rush

If we look up the spell Telekinesis, we will see that it does have an effect similar to wind blast's:

Combat Maneuver: Alternatively, once per round, you can use telekinesis to perform a bull rush, disarm, grapple (including pin), or trip. Resolve these attempts as normal, except that they don’t provoke attacks of opportunity, you use your caster level in place of your Combat Maneuver Bonus, and you add your Intelligence modifier (if a wizard) or Charisma modifier (if a sorcerer) in place of your Strength or Dexterity modifier. No save is allowed against these attempts, but spell resistance applies normally. This version of the spell can last 1 round per caster level, but it ends if you cease concentration.

The text of that ability is very similar to wind blast's, and not only that, being a 5th level spell (for wizards and magi) the concentration DC for that would be 15 + the level of the spell you're casting.