The post below is pretty clear. Still, let's clear up confusion. "Po" will denote "Plane of", as standard in EQ.
Basic idea:
PoSky, PoAir, and PoStorms are all very different planes.
What are they?:
PoSky: Classical plane. Accessed through a Wizard spell, or, more recently, it may be accessed through handing a regant to an NPC in PoKnowledge.
PoAir: "Elemental" tier plane from the PoPower expansion.
PoStorm: Second tier plane from the PoPower expansion.
Why the confusion?
In orginal EQ, there was only PoSky. When zoning into PoSky, it would tell you that you entered PoAir, and the /who command would tell you that a person's zone was PoAir as opposed to PoSky. They were, orginally, one in the same, so Verant (the then-owners of EQ) never bothered to change it. Now Sony (the now-owners of EQ)has come along and added PoAir, causing PoSky's nickname, PoAir, to be a misgnomer (have to love this word when writing of EQ).
In short:
This zone, in which this post is in response to, is Plane of Sky. Plane of Air and Plane of Storms are both different zones.
Afternote:
To those who thought PoAir and PoSky were the same, you were right.. just.. it changed. That's the one thing everyone's been missing. PoAir was the secondary name for PoSky until a proper PoAir was released.