Arguing with my brain (and losing)...and a plea for help!

I've been working on my current short story for too long.  

I know the story, like the story, but am having trouble moving it from my head to my laptop.

I think that the reason for my difficulty is that I've been thinking about the next Tyler Cunningham novel, and it's taking up a lot of mental real estate.  

I can picture the entirety of the story arc for the next novel, tentatively titled, "Caretakers" (in my mind, and in SmartPig meetings only). and keep writing chunks and sequences while driving to work or cooking dinner or watching TV or making coffee in the early morning quiet with my dogs.  

The short story I'm actually writing at the moment is an untitled piece that relates the story of Tyler's first case, and brings to light a few characters that are a part of his small and peculiar social world.

The two writing projects are vying for primacy in my brain, and while I want to complete the short story first (it's about 30% through the first draft at the moment), "Caretakers" is beating the inside of my skull like Athena, ready to be born.

I'm unsure what is the right thing to do.  A part of me wants to work through the dueling stories to finish the short piece.  Another part of me wants to embrace the novel project, and move forward with that, ahead of my schedule (I had planned to outline during July, and write "Caretakers" during August). A third option would be to do the outline and some planning work for the novel (to a greater or lesser extent), put it away, and finish the short before actually starting serious work on "Caretakers" for the summer.

I would love to hear your thoughts about which path you would follow if you were (or have been) in my place.

Thanks,

Jamie