We did the last
DCL cruise to Alaska this season. The weather was generally miserable with plenty of rain and the temps ranging from 1C - 15C, but we knew that was a possibility and we still had a great cruise !
We dressed in layers and took them on and off as needed. Having good rainwear and insulating layers was imperative.
Some excursions were canceled, though none of ours were - we deliberately chose ones that had a high liklihood of being able to happen. One family we met had three of their excursions canceled. As another poster noted, the shops in ports had some great sales.
One thing that we were not pleased about is that DCL was already sold out of almost all of the Alaska and 25th merchandise before our cruise even sailed. So things like the Alaska tumblers and blanket were not available at all. Very disappopinting as the DCL souvenirs we really wanted we couldn't get; in the end as a result we spent very little in the on board shops.