Hi! I suppose it depends on what you plan to do in Paris, if you are planning on strolling around and mainly staying outdoors then it may well be best to go when the weather is better. If you are planning on going to indoor attractions such as museums then I don't suppose the weather would make too much of a difference. However either way if there is very poor weather forecast for the Friday, and you have to travel back to a hotel near DLRP it may well be best switching to Thursday! There is plenty to do in DLRP in the rain as well, last time I went my Fiancee and I had just got on the Indiana jones rollercoaster and it started pouring it down! Not a good ride to be stuck on in the rain but it added some fear!