Judy, welcome to Cruise Chat.
The real key for dressing in Alaska is layers. Layers offer the most in flexibility and warmth when needed. The weather can be cool and rainy, for at least some of each day. When you're on the ship, cruising past glaciers, you're going to want to be outside, on the deck, watching the scenery go by. Those outside deck areas can be very cold when cruising past or anchored near a glacier, but being outside is something you don't want to miss.
"If you can't see the mountain tops in Juneau, it's raining. If you CAN see them, it's about to rain."