Alaska-Spring or fall and why

This is one of those "it depends" questions; mostly it depends on you. What do you want to do? If you are wanting to fish for salmon (a frequent goal of those visiting here) then late May through the first of September will be your best time. Earlier and you may encounter ice on the lakes. It can snow any month of the year but lately the snow season has been over by May and not returned until October. Want to avoid crowds? Come before Memorial Day and after Labor Day. One problem you can encounter both late and early is campgrounds begin to be closed. With the drop in oil prices, one of the first budget items to get cut is State Parks. Feel free to PM me with specific questions. Regardless of when you come, you'll really enjoy Alaska. It's a special place.

Edit: And BTW we're headed to Montana in September. Going to spend some quality time in Glacier.