Here’s how to predict the weather at WDW – look outside. I’m pretty much serious. I’ve gone to bed expecting one forecast – and the next morning – it’s VERY different.
If its raining before and at RD – that increases your chances of having some AWESOME short lines for a couple of hours. Typical advice would be suggest either PP or SM first – then pick things indoors. Everyone is going to do the same thing….. but if its raining enough – some folks will stay in bed longer. Since I don’t ride SM and I usually get a FP for PP – I’d probably start my day at POTC and depending on the weather – move next to JC or HM. But others might start with SM, Buzz, PP, Pooh.
I might consider bringing a change of clothes if you are staying the whole day. Or at least wear clothes and shoes that can be soaked all day. And maybe carrying an extra plastic bag or two. It’s nice to be able to put wet ponchos into a bag to store them when you are going to be under cover for a while. Rain can also make it cooler – so you might need an extra layer of clothing. And we use umbrellas to get from the bus stop to tapstiles (and put them away in a plastic bag in the backpack we likely carry on rainy days).
I’d also debate about adding a TS lunch if you can still get one. Just be warned that being wet and in the blasting AC don’t mix well – so if you do this – have something dry to put on. I say this as its nice to really be out of the weather for an full hour+ when the day is drab/raining.