I'll second what Lori and Jimshaw said. I once survived a two day hard rainstorm on Easy Ridge in the North Cascades in a highly rated bivy (for 1968). By the end of the second day I was cold, wet, cranky and bored. Since that adventure, I have never wanted to rely on a bivy setup unless the weather forecast called for a 100% chance of sunshine. If I want to suffer, I will suffer in the comfort of my own home, not in a bivy.