If you've been searching for the best source of information and stimulating discussion related to Spring/Summer/Fall backpacking, hiking and camping in the Sierra Nevada...look no further!
Temps at altitude have always been tricky for me. I camped 8-10k feet (Tenaya -> 10 Lakes) 4th of July weekend and was way too hot in my winter bag. I was surprised but sorta happy that I didn't need to always bring my winter bag. We had even made a last minute stop at REI to pick up an extra layer for one of the gals when I told her she didn't have enough insulation. I had to eat my words.
A week ago we spent a few nights in one of the campgrounds just outside of Tioga pass along the Lee Vining which is about 7k feet i think. I brought my summer bag and froze. I resorted to combining my bag with my wife's for body heat and even bought a Yosemite sweatshirt at the Tuolumne shop. I felt like a total noob tourist
At lower elevations, say 6k feet and down I feel confident bringing a summer bag.
Hiking and camping in the Bay Area and up the Pacific coast. Backpacking in the Sierra Nevada mountains. Catching backcountry trout. I write articles, stories, guides, and how to's for exploring the outdoors. http://www.loveto.camp
I can answer to the nighttime temps on August 7 and 8, based on in-tent temps taken off the watch set in my sidewall pocket: 31 at Emeric Lake and 28 at Lyell Fork near Ireland Lake trail. At both locations, our bear canisters were frosted and, at Lyell, the tents in open air were, too.
I use a Big Agnes down bag, a product known to be less insulative than the ratings they advertise. 15 degree bag was just about at comfort limit those nights, on an insulated pad and with a skin layer worn. A compatriot in a synthetic BA rated the same, chattered teeth all night and our Scouts in Cosmic Down 20's said they were cooler than they liked.
There is more discussion on sleeping bags on the equipment forum. In a nutshell, sleeping bag ratings assume a pad with an R-factor applicable to the temperature, a bag that fits properly (not too big with a lot of air space), entering the bag properly warmed (so your body heat can warm up the air inside), being properly hydrated and fed (need to produce energy all night), and the bag hood fully cinched up around your face. All of these criteria are rarely met so most people need a bag rated for about 10 degrees cooler than conditions. You are not going to get hypothermia in an under-rated bag but you will not get a good nights sleep. It is always a balance between staying warm enough most nights to sleep with a bag of less weight than you would need for the most severe conditions.
I think a lot of "kids" bags are really poor. If I were taking out a kid, I would give them one of my better bags to use.
