100 Mile Wilderness Clothing

Wait and see what the weather forecast is a few days before you leave. You don't need to plan so far in advance.

Tbh I'd be more worried about getting in shape and keeping pace.

Warm days, cool nights, not much rain. Wear orange.

I finished the at last year on September 27th using a 40° quilt no problem. I had two alpha fleeces and some light leggings for layers and that’s it. I was plenty warm in the 100mw. But I also agree with another comment that it’s so far away there’s really no point in thinking about it now.

That can be tough, because like you said it's pretty unpredictable. Both times that I did the HMW it was the end of August/beginning of September, but I've spent plenty of time elsewhere in Maine and in the Whites later in the fall. The HMW isn't particularly high in elevation, nor is it exposed. A 20 degree bag sounds like a good choice. I'd probably bring shorts and a long-sleeved merino T-shirt to hike in and plan to sleep in grid-fleece tights and my alpaca hoodie and dedicated sleep socks. And I'd carry my puffy for mornings/evenings in camp. But that's just what I'd plan, thinking about the clothes I own.

It depends on how cold you run. Have you done many nights out in your 20 deg bag? What time of year? What elevation? Were you warm or cold? And adjust from there.

Alternatively, could you camp out in your backyard or on a local trail a week or two before the trip and see how you feel?

Or if you really just don’t know what you need then take a bit more than you think and then at least you won’t be cold. The weight investment of an extra layer is honestly minimal, and you’ll learn more about your needs for the next trip.

Something like, alongside your 20 deg bag: dedicated merino wool sleep thermals and socks, a fleece or woolen midlayer, and a puffy. Take a beanie and a spare pair of socks, and lightweight gloves. That should suffice for 99% of people. And make sure you have a decent sleeping pad as well! No amount of layers will make up for pissing your heat away into the cold ground.