Alaska is a huge state, are you asking for anywhere specific (like the inside passage?). You can click on the "search" on the menu line above, type in weather, and probably find more info than you really want! Good luck.
Still decent- I have cruised mid to late August the most. expect 50-65, possible rain, dusk 9pm. DRESS appropriately - I like the cheap walmart long poncho, very compact. knit hat and gloves are a must for any outside deck viewing. Forget the winter coats- I really get a lot of use out of my removable lined nylon jacket.