Help with warmth layers for September JMT

You’ll be fine with the above, don’t overthink it. If you get cold just keep hiking. Or start hiking. Unless there’s a big snowstorm which could happen so be prepared for that.

This would be a little warm for me this time of year. I’d probably wear the long sleeve merino while hiking and leave the short sleeve at home, or wear the short sleeve and leave the long sleeve at home. I  could see the short sleeve merino + fortez being a pretty versatile combo for high elevations along the JMT in Sept.

When I’ve been in that area in Sept highs have been in the 60s F, low of around 30 F. The coldest I remember it getting was 25 F in the middle of the night and hovering in the low 50s during the day. I would encourage looking at the weather stations in the area to see what the real data is.

I would not bother with the fleece. I probably bring the long sleeve shirt for sun protection and lose the t-shirt.

You left off your sleep shirt, but that could be relevant. My “sleep shirt” is typically a Patagonia thermal weight hoodie. Combined with a windshirt it’s really quite warm and lets me bridge between featherweight shirt and a puffy. I feel free to use it during the day if needed. Since I run hot I have  sometimes dropped the puffy on extra light trips. If it gets  particularly cold I just wrapped myself in my quilt.

You could definitely leave the short sleeve shirt or the long sleeve home, as Ryan suggested. I tend to wear long sleeves for sun protection so I’d likely leave the short sleeve shirt home. If you want to go really light you could also leave the fleece home if the forecast is good (but definitely bring the long sleeve shirt in that case), depending on how long you’re planning to be out and how much you trust the forecast, etc. September typically isn’t super cold but you could get a surprise storm that dumps 6″+ of wet snow – I’ve seen that happen on labor day weekend at 9k feet in Tuolumne meadows. But if you have raingear and a windshirt plus sleeping clothes you do have some backup stuff to add warmth if needed. If you’ll be hanging around camp a lot then the fleece will be nice for extra warmth in camp. If you are hiking longer days and not spending a lot of time stationary in camp then you may not need it, especially if the forecast is good.

I hiked some of the JMT section in Yosemite Valley (out to Half Dome and around that area) last september (early september), and remember it being quite warm, high forties at night, 80’s in the day. Is the rest of the JMT much different? Later September can be a bit cooler, but of what you listed, I’d ditch either the LS merino or fleece(either/or) and the Rab hoodie, and sub in a waterproof layer of some sort. This would cover you unless you run really cold. I would sweat like a pig in what you’ve listed unless I was going really slow. The hoodie would be a good thing to keep for camp if you are going to be hanging out for any period of time outside your sleep system.

Thanks for your comments, Michael.  The valley is one of the warmer (warmest?) parts of the JMT, so that is probably not super-predictive of the conditions one might experience on the whole trail — especially the storms that start to rear their head late season.

I wouldn’t normally hike in either the fleece or puffy, but take some of the longer mileage days add the shorter daylight hours and maybe sprinkle in a cold front, I may need to.

“September” is vague. Only in the last week would I consider the fleece, and even then, probably not…

Old school rule of thumb for the Sierra.

One light layer for every 4000 ft of elevation including sleeping gear.

example, Yosemite valley- long sleeve wool shirt

Tuolumne Meadows- add your Puffy

Whitney- add another layer- for me  it would be a very light fleece layer which would be my sleep shirt too.

I have had water bottles freeze solid on the JMT and had been in snow on Whitney in August, but the cold weather did not continue past a couple of days.