None of my dogs like going out in the rain! Little prima donnas! LOL I have found consistency to be the best solution. If they potty in the house, I say No and take them right outside....every time. I also use a timer throughout the day when puppy training. That way, I never lose track of time. Eventually, they get the idea that potty happend outside regardless of weather conditions
They will now do their business fast when it's raining to get back in the house faster! LOL
Good luck!!