Transitioning to winter hiking (long, sorry)

You could use your existing layers and then stuff your sleeping bag under your shell for more warmth. I do that sometimes, but usually I get by fine with my $20, 2 pound discount store down jacket along with my other hiking layers (fleece).

I haven't invested in insulated pants yet because I sit around a fire. If not, time to crawl into my sleeping bag.

You'll likely want some waterproof gaiters, and snowshoes for the occasional deep snow.

You might want to upsize your footwear for a thicker sock. I've used trail runners, GTX socks, and mid-weight wool socks with oven bag or neoprene sock vapor barrier liners down to 10F while moving. I don't have long before my toes start freezing. Below 20F, I'm likely to be using a waterproof mukluk-like system with removable liners anyway because it's so much warmer and about the same weight as light winter hiking boots.

I use a Steripen Adventurer Opti in winter if I'm treating the water at all. Always use Energizer lithium batteries, and you should be ok on battery life. In winter, I generally carry spares because it's not that much more weight. I keep it in a jacket or pants pocket if it's below 10-20F. The manual says the minimum operating temp is 4F, but as long as the device is warm enough, it'll work.

I use a white HDPE wide-mouth Nalgene containers because they're fairly durable, the Steripen fits, and the wide cap is easier to open when frozen. I put it on a neck cord inside my jacket if cold enough to freeze. I've also made an insulator from cheap 3/8" blue foam CCF and Gorilla tape for carrying the bottle in my pack if desired. Usually, I carry a 0.5 liter Nalgene in my jacket, a 1 liter in my pack, and a 3 liter Nalgene Cantene (wide mouth) for more water or for around camp. If there's clean snow available along the trail, I eat snow frequently while hiking.

Use at least a 1 liter pot so that you can melt snow if desired, but that assumes you have something other than an alcohol stove. If using a regular gas canister, keep it warm in your jacket/sleeping bag.

For gloves, use a liner and shell system with two liners. Without liners, it's nearly impossible to dry gloves outdoors. One liner will be wet and drying inside your jacket. I use military surplus wool liners and goatskin/cloth leather winter work gloves with the insulation cut out. Slap the wool liners dry against a gaiter or smooth tree, and they turn from wet to just slightly damp. Below 10F, I use the wool liners inside either a pair of Thinsulate hunting mittens or cheap suede leather mitten shells with synthetic shearling liners.

I agree with everything Andy said. Lots of good info. I will just mention a few other bits I have discovered.

Shelter:

If you are expecting a dencent amount of snow you may want to consider some type of snow stake or snow anchor for the duomid. I doubt the Lawson stakes will get the job done in those conditions, especially if the wind picks up.

I dont see the need to purchase a bivy sack. Since the duomid can be piched down to the ground you shouldnt have to worry about wind or snow getting to you.

Clothes:

This feels like a lot of clothes to hike in. I typically will only wear one or two wool tops and if its snowing my light rain jacket, for my legs I only wear my regular hiking pants and rain paints + gaiters if I expect deep snow.

WHen I get to camp I will strip off the top I wore hiking in and put on my dry layer then with the rest of my "camp" clothes as I need them.

I am a big advocate of several light/loose fitting layers. They seem to keep me warmer than heavier tight fitting ones.

I have never used or felt the need for insulated pants at those temps.

As Andy said Nalgenes work well in winter as you will get some slush in your bottle. Steripens are my go to below freezing.

I go crazy with gloves, two liners a light waterproof outermitt, and heavier winter mitts. I dont use the heavier winter mitts too often, but I like knowing they are there in case I wet out my liners or get my hands too cold.

I dont see anything for your neck/head. I love my smartwool balaclava paired with a light beanie and add an even heavier wool hat in colder temps. When it gets close to or below zero I will add a light face mask.

Hope this gives you some ideas. Good luck!

well here's a long winded response back :)

I think the Circuit should have sufficient volume for winter trips: done

your sleeping bag is a good one: done

pads- I think the zlite and neo should be more than sufficient to 5 degrees: done

the Duomid is a great winter shelter; if you're in snow, get some snow stakes, tyvek makes a great ground cloth- I put a grommet in each corner and a little shock cord, easy to setup and stays put: pretty much done

I really don't think you need a bivy

clothing is where I think you need to get dialed in

for 5-50F on the move I'd wear a light wool base top (I like the Ibex Indie because of the hood), a light wool base bottom, a windshirt if needed, a light to mid-weight Schoeller pant (something similar to Patagonia Simple Guides, light wool beanie, light wool gloves, tall wool socks, mid gtx shoes (it's the only time of year I'd suggest gtx)

if it starts raining (or wet snow) add your hard shell and eVENT mitts

if you're too cool on the move, add a light fleece (100 wt) pullover or syn vest

if you're on snowshoes and the temps are going to be closer to 5 tan 50, a pair of 40Below neoprene over shoes are pretty nice; if not than as suggest above- a slightly oversized shoe w/ a VBL setup is pretty effective (very thin liner, VPL, warm wool sock)

carried- a warm mid-weight down parka (something w/ roughly 6-8 oz of down) should be in the 1 lb range total (FF Helios, MB Mirage or Frost Line, OR Incandescent, Rab Infinity, others)
mid-weight fleece or wool mitts, can be used on their own, with the light gloves, with the eVENT mitts or all three
balaclava mid-weight wool or fleece

if your fleece pants aren't warm enough at camp, then down pants might be what you want-I think the goosefeet ones are by far the best bang for the buck, fully custom dimensions and you choose how much down fill

for around camp down booties w/ over shoes- again goosefeet is tough to beat

spare socks

Nalgenes in the winter, I'm usually melting snow for water, but I carry micropur tabs if there is no snow- filter and even a steri-pen is a little risky in winter imo

you don't mention your cook system, but an inverted canister setup is a good (and easy!) way to go, if melting snow is going to be a possibility I'd suggest at least a 1.5 l pot

don't know what kind of snow you might expect, but I always carry a small shovel (about a pound)-absolutely needed for a snow trench or snow cave shelter, but I find it useful even when using a tent- if there isn't much snow however, just dead weight

Agree on most everything here, personal preferences being the only real differences. I could make any of this work.

But, agree to nix the bivy… Redundant with the Duomid and ground sheet.

If there is snow, I don't carry stakes at all unless camping above treeline, which I almost never do.

Just make deadmen from sticks, using a slip hitch of some sort (I use a mooring hitch) to attach the guylines, and leave the un-knotted tail uncovered so that it can slide around the stick easily when removed, leaving the stick buried in the snow. The sticks don't have to be huge… 8" long with 1" diameter is plenty in most cases. Just pack down the snow and let it consolidate for a while before tensioning the guylines.

If the tail won't pull out easily when you're ready to go, wrap the guyline tail around a stick to get a more solid grip on the line (last photo).