The Norwegian cruising season is usually Mid-May till Mid-September. Check cruise lines websites for specific dates or specific ships. The weather in May & June can be excellent. This year they had temps of 80 degrees F in Stavanger in early June.
They are going to the Fjords from late May through the summer. I would suggest that you go to their web-site seabourn.com and have a look for yourself. …. Neil.