Although I've never cruised to Alaska, our son and wife did in July for their honeymoon. They packed warm clothing and used it!!! Sweatshirts were the order of the day, they said it rains (drizzles) and it was cool. Not like a Caribbean cruise for sure. Enjoy your cruise!!!
I cruised though the inland passage from Vancouver to Alaska many ( approx 10 ) the 3rd week of June. I was on a small Cunard Lines Ship. It did have a pool but it was barely used. The weather was nce but not hot. Dressing in layers seemed to be the trick.
Mornings and evenings wer cool bu it was nice during the day. It only rained part of 1 day. Bring sweatshirts, light jackets and a light vinyl rail parks that is easy to pack.
Be prepared to see some scenery that it unbelieveable. Dont forget to go the the Red Dog Saloon and have a cold one.
I will be on the Golden Princess 7/25 in the S. Carribbean to see what it is like on the other side of the world.