I pretty much agree with Wayne, You need to bring like a sweatshirt and some pants/jeans, w/e. But some days it will probably be warm enough to wear a shorts and a t-shirt. The weather in Alaska was pretty different on my trip, from 80 F (27 C) in Vancouver to 60 F (16 C) in Juneau and maybe a low temperature of maybe 45 F (10 C) for me which was in Skagway/Glacier Bay. Unfortunatly you probably need to bring both warm and cold stuff cuz it totally depends on the weather which can change pretty quickly. Also, as a general rule, it rains alot in alaska so bring stuff so that you dont get too wet while your on shore excursions or whatever, but always hope for the best cuz its really beautiful when its sunny (especially on the inside passage)
Have Fun Jenna!!!