Alaska is never a balmy state, even in the summer, and since most of the cities are along the coast, expect a pretty consistent ocean breeze to cool you off still further. That's not to say Alaska isn't beautiful this time of year.
High temperatures will be in the 60s, lows in the 40's, with those numbers dropping the farther north you go. Also, summer is one of the rainier seasons in Alaska, so plan on bringing not only some warm clothes, but some rain gear as well. Add an extra measure of all of these if you plan on being out on a boat, or hiking in Denali, for example.