Here's where my taking six months to router, sand, stain and varnish the lumber for my bookshelves comes back to bite me in the ass. The 2"x12" boards I'm using for the uprights were stored outside that entire time as I worked on them. Now, they were stored under cover out of rain and direct sunlight, and on 2"x4"s to keep them off the concrete, but the changes in humidity and temperature still had an impact. Two of the boards, in particular, showed significant bowing (significant being 3/4" for one and almost 2" for the other). For most of them, this wouldn't be an issue, since shelves on either side of them would force them straight. But these two... one is on the side of the corner cabinet, abutting the house support column with makes that wall irregular, and the other is the end piece closest to my office door. This is problematic, since there's not any shelving on the other side to force it straight. Because of the bowing, the carefully measured and cut shelves don't sit securely in their dado slots. See?
Chicken Ranch Central