A couple of years ago, my ride partner and I were on a three day ride with what amounted to a perfect weather forecast. Well, that forecast turned out to be 100% inaccurate for both rain and temperature. The first day, it rained sporadically and we managed to find shelter along the way and avoided the heavy stuff. We spent the night at our scheduled B&B a bit worse for wear.
We awoke to grey, sullen skies with the rain starting within minutes of hitting the trail. After about an hour, lightning began crashing down along the wooded trail we were on. Soaked and getting more and more cold, we continued on until lunchtime. At a restaurant, we ate hot meals and begged for a couple of large trash bags and fashioned them into ponchos which helped tremendously in dealing with the rain, but especially the cold (and this was in the US in July!). Five hours later, we made our next B&B and used the laundry facilities to clean and dry out our clothes. It stopped raining 30 minutes after we arrived!
I guess the bottom line of our experience was a) don't trust the forecast, b) carry a bit more clothing options than you think you need, c) keep calm and carry on. Riding in the rain on a limestone trail was not pleasant but, in hindsight, it's the thing we joked and talked about later, whenever we reminisce about that ride.
This line from "Young Frankenstein" got used a lot:
