Ditching fleece for high Sierra conditions

I would not bring a fleece on the JMT in august, unless the forecast looks especially wet/cold. I would bring 2 shirts – a short sleeve and a long sleeve shirt of whatever type you prefer. I have done a number of trips on the JMT and this is what worked well for me in july/august/september (for trips up to 9 days in generally good weather):

capilene 1 T-shirt
capilene 2 zip neck shirt
light synthetic or down puffy (I have used a few different ones – MH Compressor, Nano Puff, Ultralight down hoody, Atom LT, etc.)
Light rain shell (OR Helium 2)

In late sept/oct I would likely replace the cap 2 with an R1 pullover or hoody, and bring a warmer puffy as temps are likely to be colder and storms become more likely.

You may want to go with synthetic puffy and/or fleece for a longer trip as you are likely to get some rain. However, sustained rain is not that common (it does happen though!) so chances are you'll be able to dry out the down if it does get wet. This is not guaranteed however so synthetic is a safer choice especially if your bag/quilt is down.

having 2 shirts allows you to wear either one or both as conditions change. It also allows you to have a dry one to change into when you go to bed and/or get to camp and put the down jacket on which is nice. I personally would worry more about the down getting soaked from sustained rain than putting it on over a sweaty shirt.

On the other hand, if you are out for a 3-4 weeks, and spending a lot of time stationary, a synthetic puffy and/or light fleece does give you a bit of insurance in case your down gets soaked.

My layering system for the JMT last August:

– REI Sahara Zipoff Pants
– Smartwool PhD Run L/S Zip Top (merino blend, about equivalent to 150 weight)
– Marmot NanoWick Windshirt
– Frogg Toggs UL2 Rain Jacket
– Uniqlo UL down parka (probably about 2.5oz down fill)
– Knit beanie
– Merino Buff
– Fleece gloves
– Icebreaker 150 weight long john bottoms (for sleeping/camp)

That's it. No extra shirt, no fleece, and a lighter down jacket than the Alpine Light. And I was perfectly comfortable, even when I stayed up well past dark. The moisture from your sweat probably won't kill your down jacket as quickly as you think so long as it's only residual sweat (if you're making MORE sweat while wearing the down jacket, that's a different story). But I normally didn't go straight from active hiking to my down jacket. I'd put on my windshirt when I got to camp, which would let me cool down and dry off a bit.

If you are worried about a sloppy base layer, why not carry a spare silkweight top to wear with your down and sleep, giving your "active" top a chance to dry, or even washed and dried. That would be lighter than a fleece and you could still wear it with all your other layers if too cold.

I usually take my shirt off right as I get to camp. Sometimes I'll even rinse it in a lake/stream at that point, and lay it on a warm slab of granite or hang it up to dry. Things dry very quickly in the Sierra. If there are mosquitos or another reason I feel the need to wear something, i'll put on my windshirt while my nylon hiking shirt is drying(a little clammy but it works). Shortly before dinner time, I have a nice clean and dry shirt to put on under my down jacket.

I always need the warm fleece layer in the morning when it is the coldest.

–B.G.–

"For this condition, I'm thinking about leaving fleece at home and bringing: light-colored 150 merino long sleeve top, MB Alpine Light jacket (4 oz fill) and rain shell. I also have a down hood, 150 merino longjohns and rain pants as part of my night/sleeping/rain gear."

"My logic is based on the idea that high Sierra has rapid cool-down and heat-up transitions, and that I will be doing strenuous hiking (with pack) in day and more passive photography (maybe with some careful rock scrambling) after cool-down. So day-wear is just my shirt, plus rain jacket if needed for rain or wind."

I don't hike in the Sierra Nevadas, but I do hike in cold/wet conditions. Based on what you wrote here, I'd bring the down. If I thought I'd need to wear insulation while hiking, which would be well below freezing for me, then I'd bring the fleece.

My reasoning.

If it rains while you're hiking, you'll likely be plenty warm wearing what you have minus the down which will be in your pack.

If it rains in camp, it'll be too cloudy to watch the Perseids so you'll be in your shelter.

If you need some warmth and you're sweaty/nasty from the hike, wear the down over your rain jacket.

The conventional wisdom for the PNW forever and ever has been that it's too wet up here for down. I finally made the switch from synthetic to down after joining BPL. I've been in some hellaciously damp humid cold rainstorms with condensation splattering on me from my tarp and haven't had an issue with loft yet. Yes it does require some care but for me, it's been easy to manage. YMMV.

Don't forget, if all this fails, you can wrap yourself up in your sleeping bag.

Again, if I think I'd wear it while hiking, then fleece is what I use.

In wet weather, a down jacket has never been an issue for me. I only ever wear down once I set up camp. When I stop for the day I strip off all of my damp clothing and put on my down jacket. Then my rain jacket goes over the top. So I can walk around outside my shelter and do whatever without getting my down jacket wet. I might get a little perspiration trapped in there because of the not very breathable rain jacket but not too much.

Thanks all! Lot's to ponder here.

Man, I got my MB Alpine Light today! This is one freaking nice jacket for $122! It would be way too warm to wear while hiking almost anywhere, but it may do me well for nighttime photography at 12000 feet. Fortunately, I'm living in the middle of a polar vortex now so I can test it out tomorrow at the bus stop.