We had several days of rain on our Alaskan cruise.
When we were in Juneau, it was rainy, and 38, took the tram up to the top of that little mountain, and there was 10' of snow and still snowing up there.
Rain or not, it's a great time. Lots of whales will be spotted throughout the day when cruising, she always kept the camera on her for that reason. When we got to the glacier, there was a million little seals playing on it, very cool to see in person.