I do some winter/snow trips every year, but am not as experienced or expert as many people who live in cold climates.
I have found that almost nothing I use in 3 season hiking works in winter, except my Houdini Wind Shirt, and occasionally a pair of running shorts and a very light down mid layer. In winter it is critical to stay dry and warm. Also I have found that conditions really vary from trip to trip, and longer trips require me to be prepared for changes in weather. So the first order of business would be to determine expected weather, which IMO will affect what gear you need.
- Temperature range (expected highs and lows)
- Precipitation during the day (rain, sleet, snow, none)
- Terrain (snowshoes, crampons, heavy exertion, easy exertion, other)
The big thing for me is getting the right layering so I don't sweat (or sweat very little) while hiking. And I add/remove clothing more often than during 3 seasons, especially if the wind comes and goes during the day.
Typical clothing items are:
- Capilene 2 or heavier (sometimes hike only in the top)
- R1 Hoodie (not always worn)
- Houdini Windshirt (not always worn)
- Schoeller Fabric Pants (light or heavy versions-these are water repellent)
- Running shorts (sometimes hike only in bottom base layer - these are a modesty item)
- High GoreTex Gaiters
- Thicker wool socks
- Silk sock liner
- Rocky GoreTex Socks
- Breathable Trail Runners (one size larger than normal))
- 2 or 3 pair glove liners (they will get wet)
- eVent Mitts (GoreTex gloves always seem to leak)
- Puffy down Jacket
- Down pants
- UL down jacket (sometimes)
- Waterproof shell for upper
- Waterproof bottom (rarely used)
- Down booties
What drives me nuts is the precipitation. Wind blown rain and/or sleet is miserable, wet snow around freezing point gets clothes wet, snow in the low 20s is best as rain gear is not needed.
For an upper shell I often use a poncho. Works better than a lot of folks would think. But not always ideal. For 3 seasons sometimes I use a Marmot Essence Jacket, but most often a poncho. The Essence is too small with additional layers, so I ended up buying a Marmot Ageis, which has the same membrane as the Essence. A little heavy, but it works for me and I did not want to buy an expensive eVent shell for limited use, nor do I want a 3 season shell that is way too big.
I almost never wear any down garments when hiking. But at rest stops I have to put on a down jacket, which is usually a NB Fugu. Sometimes when I know I will be traveling in very cold weather, with low exertion and a lot of navigating I will wear a Montbell Ex UL jacket and this winter may take my new Montbell Ex UL vest. Some trips I end up with two down upper garments; a light mid layer when hiking and a big puffy for stops and camp. I live in a desert, so I do poorly in cold weather.
I only use the down pants in camp. Sometimes I will sit outside and cook, so I sit on my foam pad. I also always bring an insulated air mattress, which is another non-3 season item.
Now for the upper shell. With gaiters and a poncho no rain pants are needed. Sometimes with a rain jacket I will use some sort of rain skirt if the precipitation is wet. Again this varies by trip. If I am using a poncho and snowshoes will be strapped to my pack part of the time, it is going to be an inexpensive silNylon poncho, because the snow claws on the snowshoes can damage the poncho. This year I have been doing a lot of poor weather 3 season hiking with a zPacks poncho/ground sheet. This is smaller than a typical poncho and has done well in cross country travel. But I am not sure if it is big enough to cover my larger winter pack, and I am not going to risk it covering snow shoes.
Since most of my backpacking is 3 season, I don't want to use heavier dual-purpose winter stuff that is much heavier. So I am willing to buy heavier gear for winter only trips.