I am planning to spend (for the first time) the week of May 14th thru 21st in Yellowstone/Grand Tetons NP's, seeking striking/dramatic landscape images.
Hi Quentin. You should be mostly OK with the roads. Beartooth pass will likely still be closed, however. And according to the Yellowstone NP website, Dunraven pass (between Tower and Canyon) isn't scheduled to open until late May. Snow storms can hit at any time, of course. Also, be aware the Artist's Point canyon overlook, and the road up to it, are under reconstruction. I'm not sure it's scheduled to be finished by May of next year, so definitely call the park to find out.