One more thing I've learned the hard way about group rides in the rain -- follow your own judgment, not what people around you are doing. If the rain and/or wind is strong enough that you don't think it's safe to continue riding, stop riding. Find safe shelter (NOT a tree!) if you can. But just stopping on the side of the road during heavy rain to wait out the worst of the storm is better than trying to stay upright and continue riding in bad conditions.