Interesting. I just spoke to some customers where I work tonight that have just come off an inside passage cruise. I asked them the same thing.
They told me they never wore shorts, but were never very cold. They said they were lucky because it didn't rain. They said they would never hang out at the pool, but were never freezing.
first let me say you are going to love this cruise and be taken in by the beautiful scenery you are going to see. i was in the inside passage in the middle of sept last year. the weather was very nice. i wore a sweatshirt with a lightweight nylon jacket over it on the day we were in the glacier bay. other wise i only wore the sweatshirt or a sweater with jeans or comfy pants. take a turltle neck if you are cold blooded with a very light weight jacket and some pants. also dont forget a few pair of shorts. it is summer there then. i took a pair of gloves ( the one size fits all type and a headband for my ears ) and never used them. also the umbrella stayed in the cabin. it only drizzled in ketchikan and the hood of the jacket was enough to keep my dry. alaska is more casual than some cruises. so i have read. sunday dresses and pants with nice tops for dinner, capri outfits or anything that looks nice and is comfortable is the order of the day for dress on board. a comfortable pair of broken in shoes are a must for shore tours.
We were there 2 weeks ago. Bring both. Juneau was in the 80's and the cruising was in the 50's. Layer is the word. Make sure you have a jacket and sweatshirt. deck was cool, definately poolside weather when we were in port. We did wear shorts in port. Depends where you are from. We are Floridians so 60's were cool to us. Hubbard glacier was cool. Needed a jacket and hood.