When we did our Alaska cruise at the end of july/beginning of august, the weather was perfect.
We did not get any rain and it was not cold, but it was more long pants than shorts weather.
We did visit all the places that that you mentioned and we had an excellent cruise.
Carnival Liberty New Year's Eve 2007
Liberty of the Seas 5/2008+11/2009
Allure 1/16/ 2011
Vision OTS 2-14-2015
Freedom OTS 3/6/16
Booked -Harmony of the Seas. 12/31/16