I just did a ride in Yellowstone National Park and wore this jacket. It is a men's jacket, but I am sure that the Team Estrogen Ladies could help you find a comparable womens jacket;

I was so impressed. I stayed completely warm and dry despite riding in 8 miles of continuous downpour. The temps were in the mid/high 40's and I had a sleeveless tank on under the jacket.

http://www.gorebikewear.com/1164920285784.html

Good Luck!