I believe that the Astral Plane is more of a psionic world than a physical one like ours. So, maybe she connected more to her psionic energies, instead of primal energies. When you think about it, the Astral plane is all about psionic and telepathic connection, and characters like Jean, Professor X and others exceed in that and they are able to use their powers to the fullest in the Astral Plane, so I think that something like a psionic connection to that environment happened for Storm, and she was able to manipulate the Astral plane's elements.
Don't forget that psionic stands behind the psychokinesis like telepathy, telekinesis and atmokinesis which is one of Storm's capabilities. Or at least one of them. A lot of people forget that the science behind Jean and Professor X's powers and other telepaths is psionic. Ororo is a psionic mutant as well, she should be fully capable of using her abilities in any dimension or realm, since she connects with its elements on psionic level. It seems like a lot of people don't get Storm's full capabilities yet.