Riding in the rain is a really broad question. A steady rain in the 40°'s or colder, I am not going out for a long ride, recreation or training, on a regular bike. Like someone said earlier, do it tomorrow or the next day.

Commuting to work, that same cold rain never stops me. The difference is that I know that I can deal with it for half an hour, all weather conditions that I've seen in this state. But longer than that could be threatening, and it won't be any fun.

After about 70° a ceaseless rain might or might not be unpleasant and much warmer the rain is sometimes even welcome.