Irrelevant, annoying, inaccurate statistics about rarity of hypothermia:

http://www.nws.noaa.gov/om/hazstats/cold06.pdf

http://www.nws.noaa.gov/om/hazstats.shtml

Do consider that alpine camping in Washington is generally in the 5000-6000 foot range with most higher summits topping out around 8,000 feet. Only two peaks in Washington are higher than Camp Muir, which is at 10,000 feet.

Also consider that currently, for the Cascades, it's still very, very early in the season (really pre-season) even apart from the recent, extremely unusual weather.

For almost anything except Rainier summit, torso insulation layers to bring along in summer in Washington (July- Aug.) could be easily limited to a light pile jacket and a mid-weight poly turtleneck plus a light shirt. This excludes wind/rain layer, etc. A sleeping bag rated at 30F-40F can work very well, sometimes wearing all available clothing.

Obviously being prepared is important, but going overboard isn't necessary and there is a remote chance that getting exhausted from carrying too much stuff could contribute to your untimely death.