Tarp options, BPL bivy-quilt

I have not used either tarps you mentioned but I have used a MLD grace solo. I really like it because it has linelocs instead of just grosgrain loops on the tieouts. The linelocs make the set up very easy. So of the two tarps you are looking at the MLD is heavier than the GG but it is easier to set up which may or not be worth it to you. Also the MLD is available in a few weeks but it is not clear when the GG will be available this year.

I do not think that the sleep system you mentioned would be warm enough. (I am assuming that you might see lows down to freezing on the JMT) I have not used the BPL 60 quilt but I have used a homemade climashield 2.5 oz/sqyd quilt of similar CLO value and I do not feel like it would it would work well below 45 F unless I had a warm jacket like a thermawrap parka. Take a look at the Jacks r' Better stealth quilt it is probably 10 degrees warmer than the BPL quilt and still relatively cheap.

Last August I had pretty good frost several nights on the JMT. I also had a few nights in the 50's. You can often camp lower and under a tree but that may mess up your pace. I always suggest a sleep system for the high Sierra that will keep you comfortable at least to freezing.

For the JMT, I think I would choose the MLD DuoMid over an open tarp; you can completely seal it up in a crazy storm or pitch it high to vent. This eliminates the need for a bivy for spray protection. I would then choose a 20F-30F down bag so I wouldn't need the bivy for draft protection. My Marmot Hydrogen weighs 24 oz. in a long, I think a bag like this is perfect for summer above-treeline. The Duomid weighs 15 oz. in silnylon, less than either spinnaker tarp combined with a bivy, and it's more robust as well.

Okay, so I think based on these comments I will stick with a WM Highlite plus additional insulation. But then the question still remains, precip and dew protection. Perhaps I thought I read that a properly pitched tarp (in the right wind direction, pitched to the ground if need be), could keep out the rain, especially with a two person sized shelter like the spinntwin. Would an inexpensive bivy over my highlite greatly increase protection from condensation, or do you feel that to be an unnecessary addition in the Sierras? How much will lower tarp walls effect condensation production, I would think lesser ventilation would produce greater condensation, as I have seen in a 2 wall tent vs tarp tent, etc.

Thanks,

Chris

It's true you'll get more condensation in an enclosed shelter, although most provide some means of mitigating this. With an open tarp it's much less of a problem, and I typically use open tarps below treeline except in winter.

Above treeline open tarps can present some difficulty. Wind direction can change, leaving a previously storm-tight pitch vulnerable. One phenomenon I've yet to figure out how to deal with in an A-frame tarp pitch is wind from above. A few years ago in a nice little cirque in the Wind Rivers, wind blowing down the mountain into the cirque caused all kinds of problems with my tarp pitch. Something like the DuoMid is much less susceptible to these problems. Also, because of the defined perimeter, you can set up a mid style shelter super-fast, which is great when a fast-moving storm blows in.

I think in storm conditions above the treeline, the bit of air movement you can create in a mid is enough, especially with only one person fogging things up! With more benign conditions, a higher pitch and opening things up provides plenty of airflow.