15 degree bag for 3-three season in the PNW?

That sounds about like my experience in the Enchantments. The tent I was using held up fine, but it was LOUD. And drafty as all get-out. It was pretty unpleasant, but I had a warm enough sleeping back that I wasn't freezing, just awake for a lot of the night, mostly because of the noise of the wind roaring through the camp.

We started that trip in 90-degree heat, end up with freezing gales and blowing snow, and then returned to 90-degree heat for the last leg of the hike back.

The Cascades are incredibly beautiful, but they can be pretty unforgiving!

I have a 30deg. Marmot bag and that is what I use year around. If I go in the winter I take an old Feathered Friends bag (30 deg. also) which I slide inside my other bag. But that is rare…. typically I just carry a single 30deg. bag and supplement it with extra clothing when it is cold.

I hike exclusively in the Olympics and I don't find any problem with humidity. The SE USA is worse for moisture/humidity as far as I'm concerned. Our weather is mild most of the year without extreme temp swings because of the moderating influence of the ocean. Our season is short and snow is on many of the passes year around but I don't sleep in it. The eastern side of the Olympics is often very dry in August/Sept. while the western side is fairly wet year around.

Tony,

Punch a couple holes in your GG pads and run cord through them. The pad attachment system will work just fine that way.

Thank you everyone for all of the replies. This has turned into a wealth of knowledge. The general consensus seems to be that if i am out between may-sept, i should be fine with a 25-30 degree bag as long as i have a proper layering system in case it gets cold enough. So this has led me to look primarily at Western Mountaineering bags, which appear to be top notch from all of the reviews i have read here and on the forums. I think i am going to look at the megalite/summerlite and the sycamore. I am going to try and check out OMC this weekend and look at some of the bags.

Oh and i guess i have one more question. I am looking at the sycamore because i am a "4" sleeper, and wanted to know how substantial is the heat loss due to the extra space caused by the bag being wider? i am considering if it would be more worth it to just change my sleeping style for backpacking and go with the summerlite to maintain the warmth, or will i be able to get close to the same warmth with the sycamore, being 5 degrees warmer. Does that make sense?

From what I've read wm does an honest job at rating the rectangle bags correctly as well – you'll notice they're a bit heavier.