I'm not staying at POR, but I am heading down from MN!
We were there at the same time last year and we did need sweatshirts in the evenings once or twice. Not that we had them... I ended up buying one for DD because she was the chilliest. This year we'll do the same. I don't want to carry anything all day - so if it gets to be too cold, we'll spend a few Disney Dollars on a fun sweatshirt! I did put rain ponchos (Dollar Tree) in our packs. There were quick showers on three of our seven days. It didn't last long, and it was nice to throw the poncho on and then toss it in the trash. Well worth stocking up so you don't have soggy ponchos to carry around. I bought four for each of us this year. I'll hope for warm sunny days though!