I rode 60km in the rain last night. It was a tempo session and I found to my surprise that I took myself around the 30km tempo part of my route that it was my fastest time this year. I think that the feeling of being out and riding in the rain made me feel like a tough bad*ss cyclist and that feeling carried through to give me a power boost.
Make the bad conditions your friend - it's like Magnus Bäckstedt who said before Paris Roubaix this year that he would like it if the course was muddy as he loves the bad conditions and that gives him a mental advantage over the cyclists who hate the rain.