packable rain gear

I have a wading jacket that keeps me warm an snug when I use it, and I use
it gladly whenever the weather is clearly going to be nasty most of my
fishing day. But it makes me feel like a hunchback it's so large when
stuffed into that big back pocket of my vest ... so I prefer to leave it
behind, when possible.

But, last 'summer' there were many days in Yellowstone that were patchy
nasty, mostly nice but every so often a cloud would roll in and dump some
rain or snow for a few minutes. The overall temperatures are such that
getting wet is not pleasant, and I'm in the market for a very packable
jacket/poncho/something that I won't mind carrying all the time, that will
keep me dry, and that will serve good windbreaking duty when it's a bit
chilly.

When it comes to comfort, I don't spare expenses .... so

suggestions?