Clothes for Wonderland Trail in early September

Wonderland Trail early September – probably 40 F to 70 F, no rain, but sometimes it gets down to 32 F and could rain the whole time – check weather report before you go and maybe adjust gear slightly

I just wear a base layer that also provides sun/bug protection, and an eVent or Gore-Tex jacket for wind/rain protection.

When I'm not hiking, I add an insulated vest or jacket for extra warmth.

More layers than that is heavier than necesary. If you're still cold, you should use a thicker insulated vest/jacket.

Just one way to do it. You can add extra layers if you want : )

Lower Body: I would only add one light shell layer, either a rain skirt, thin nylon shell pants or silnylon chaps. Better layering, so that at least the upper part of your hiking pants stay dry and you are a little less likely to need the base layer tights until camp.

Upper Body: I would hike in the merino top, carry the s/s t-shirt if you think you'll use it but take the lightest one you own, and take an insulation layer, in your case the light fleece or, even better, buy a light down or synthetic jacket, which should be useful in the upper midwest for future trips. You do need to pack the rain shell for the PNW. It might sit in the pack the whole time, but it is just something you need to carry here. I do carry a wind shell which I think would more useful than carrying the fishing/hiking shirt.

Keep the warm cap, sun hat and add in gloves.

I haven't hiked the whole loop, just parts but there's a reason its considered one of America's premier trails! You're going to love it and that's a great time to be there.

In September it gets dark earlier up high – and the winds are usually chilly at night – but still nice in the daytime hours ;-)

So, be prepared for most anything – well besides bugs thankfully! But do make sure you will be warm at night.

The two sides of the mountain can provide you with completely different conditions. When we went 3 years ago, it was the last 2 weeks of August. The east side from Longmire to Sunrise, we had 85 degrees during the day and 50-55 degrees at night, and we were sweltering in our down bags. We had a resupply at Sunrise, and dumped some stuff. On the west side, it was much cooler, had a couple of days of misty/rainy weather, and much cooler temps. We used all our clothes. A picture of my boyfriend at North Puyallup River campground:

So, a little more insulation might not be a bad thing!

Be prepared for temperatures ranging from freezing to 85*. Last year, it was warmer for me in September where it stayed in the mid 80s for a few days compared to August where I doubt it got much over 70.

Here's what I'm wearing/bringing this year:

Worn:
Trail runners
Sock liners
Nylon pants
Running shorts
Nylon t shirt
Nylon LS hiking shirt
Sun hat (yet to be purchased)

Carried:
Rain shell
Sock liners
Watch cap
Buff
Possum down gloves

Sleeping:
Silk weight tops and bottoms
Wool socks

A couple notes on my list:

I'm comfortable in this down to freezing.
I spend most of my day moving and not in camp
I'm fine with wet legs and feet for days at a time
Nylon shirt works fine for me instead of a wind shirt in above freezing temps
I never need more insulation than this above freezing but can use sleeping bag in a pinch