I have cruised Alaska before but was later in the summer and there were occasions that shorts and short sleeve shirts were needed. Is this true in May for Juneau, Skagway. or Ketchikan?
Murray is right. You are likely to encounter warm temperatures, especially around Vancouver, Skagway, and Anchorage, even in May. Juneau and Ketchikan tend to be cooler and often rainy, even in August.
If your ship is going to any of the glacier areas, you will want a winter coat, gloves, and hat to wear out on deck in those regins. The calving of the glaciers turns the bays into ice water, which invariably has a temperature of zero degrees Celsius or thirty=two degrees Fahrenheit. The air above those bays is not much warmer.