>>2858092I'm assuming these temps are in F since you're talking about the AT. I've camped in similar conditions multiple times in a tent (with sleeping pad), hammock (sleeping pad, no underquilt), and hammock with an underquilt.
I would highly recommend reconsidering your shelter, but it isn't a deal breaker as is, you just might not be terribly comfortable. The tent + sleeping bag combo was by far the least comfortable (6°F) and I ended up putting my outer shell down over the pad to keep some of the cold out. The sleeping pad + hammock (with a warbonnet superfly) was the middle ground (9°F), more comfortable than being on the ground, but any portion of your body that leaves the pad will immediately feel it (same with sleeping on the ground). The hammock with synthetic underquilt and warbonnet superfly was completely comfortable (5°F) the entire night.
I should note that I was using a synthetic fill 0°F Ozark Trail mummy bag for each of these trips (yeah, it isn't much and is bulky but damn if the thing hasn't worked and held up over the years).
I would rethink the bivvy and rainfly for this trip, but again, it isn't like you're going to die in it, just might be a little uncomfortable at times.
I suggest bringing some hot hands, or the larger toasty toes if you can find them, and toss a couple in the sleeping bag 20mins before you go to sleep, it's a nice luxury.
Your current setup will work, but you might hit some uncomfortable moments. If this is your first time winter camping, you may be in for a little bit of a surprise with your current setup compared to warm weather camping, but again, you'll survive. Sleep in your clothes if they're dry. The wind on the first day will be the worst part, especially with your diamond fly.
