Bets to pack layers of clothes that can be easily put on or taken off.
We were on Artemis in the Fjords last week. The weather was excellent with superb scenery that looked so well in the fine weather.
The temperature in Stavanger last Thursday was in the 80s. In the other places it was in the 70s. We had fog in the north Sea both on the ooutward and ineard journeys but hardly and wind.
Don't know about the formal dress requirements but I am sure the brochure will tell you.
Have a lovely holiday and enjoy the breathtaking scenery.
However, the weather is a gamble and may be lovely or no.