There are NO sure things about weather in Alaska and most important, no way to predict. You will need to be well prepared in your attire no matter WHEN you go, including July.
Go to weather.com; type in city/state of port of call, click go; next click on "month" option. This gives you excellent info on past days, current day, as well as, averages and record hi/low temps.
The data will validate the previous posters statements. Temps can swing from hi of 90's to low 40's.