Drazelic: man, perspective is consistently my achille's heel and something I definitely need to work on. It's easy to see after someone points it out to me, but I'm blind to it far too often while working on my own! That was an incredibly helpful post, and I'll be incorporating those ideas for certain. Thank you so much!
kullenberg: the grey is actually just my neutral background color that I work with; it's not meant to represent an overcast sky. It's just empty right now. There's currently no "sky" of any sort - I was going to have direct sunlight in the final product. I had pictured this as the first snowfall of a season, unexpectedly early, and not the height of winter. I can understand the critique, but I like what I'm going for and am going to stick with it. The contrast of the leaves and the snow appeals to me.
EDIT:
After some edits, this is what we have thus far!