Incorporeal Undead Swarm vs Control Winds

[GM Rednal]

Yeah, it's an interesting situation that my players are in. So, uh... how do you guys think Control Winds would ultimately affect a creature of this type? I know undead can be affected by things that affect objects, but if the spell only CREATES the wind, I'm not sure it would actually work...

[Thanis Kartaleon]

Universal Monster Rules > Incorporeal wrote:

Corporeal spells and effects that do not cause damage only have a 50% chance of affecting an incorporeal creature.

Wind is a corporeal force (unless the caster has the Ectoplasmic Spell feat from the Advanced Player's Guide). An incorporeal creature, swarm or no, is affected by such an effect only 50% of the time.

However, the spell also calls for a Fortitude save.

UMR > Undead Traits wrote:

Undead are immune to ... any effect that requires a Fortitude save (unless the effect also works on objects or is harmless).

The spell does call for only creatures to make saving throws against the wind, and this is the same for the Wind Effects section of the Environmental rules. So, strictly speaking, the swarm would be immune.

However (again!), the Wind Effects section makes numerous references to objects being affected by the wind. Control winds makes it clear that the wind controlled/created by this spell acts just as the environmental element. And just to be clear,

Control Winds wrote:

...destroy wooden buildings, uproot large trees, and cause most ships to founder

These are all objects being affected by hurricane force winds controlled by the spell.

My final ruling: Affects the swarm (Fortitude negates) 50% of the time.