In Calgary, it rarely rains and stays warm. It can be warm, then rain, then be warm again, but almost always cools dramatically while it is raining. I usually wear full rain jacket and pants with pack cloth overshoes while it is raining noticeably, light showers I sometimes just get damp.

What you wear, depends on the exact weather patterns and your needs. The only thing I would definitely recommend is the fullest coverage fenders that you can fit on the bike. It's not only rain water you're going to get flung up at you......