I have just finished an excellent book : the ultimate hikers gear guide by Andrew Skurka. ( free, at the library) It has many crossover ideas for light gear in extreme and varied climates that easily apply to biking. He says for cheap price the polar fleece keeps you very warm at a low cost. I agree! I used a fleece jacket the other week in weather that ended up in hail. Most of the ride I had the jacket open then as the rain came I closed the zipper. I have an emergency rain cover that fits into a plastic ball that looks like a Christmas ornament. This ball I had clipped on to the back of my saddle. It is just a light almost "cling wrap" material that has a hood my helmet fits into. It kept me dry though it made a lot of noise! I got it for free at some feed store for riding horses out on trail but I'm sure you could find one at a super low cost. A garbage bag always works in a pinch too. None of these will breathe obviously. But they do keep you dry. This so far, is my best set up. I love my new windbreaker jacket, liked with wool- but it is either too hot or the lack of breathability annoys me.
It was hard to see however, in all that rain. I thought boy this rain really hits your face HARD! Then I realized it was hail! oops! How do you see well in rain, hail, snow while moving along on the bike? What do motorcyclists do?