Weather in the Baltic and the Danish Straits is greatly affected by the surrounding terrain features. The most significant feature on the Scandinavian Peninsula is the Kjolen Mountain Range which is located to the north of the Danish Straits and to the west of the Baltic Sea. The difference in weather features from one side of the mountain range to the other is extremely different. The mountains force the air to rise, causing the air to cool and lose their moisture in the form of rain. The cloudy skies on the western side of Norway gives way to partly cloudy skies east of the mountain range as little moisture is left in the air to form clouds. The mountains also stop or significantly weaken strong frontal systems moving into Scandinavia from the North Atlantic. They also trap cold air moving in from the east during the winter causing extremely cold temperatures over Northern Sweden and the Baltic Sea during the winter.
Elsewhere over the Scandinavian Peninsula and for the country of Finland, the terrain is rolling hills, lakes, streams, and marshes which tend to moderate or stabilize incoming air masses as they cool the air moving in.
Other terrain features south of the Baltic Sea and the Danish Straits do not play a large role in controlling weather features due to that they are so low lying. The only significant influence would be from the major river systems located in Germany.
The valley area has significant water sources which cool the air above which frequently produces fog over the area during the winter. A southern wind over Germany can bring fog into the Southern Baltic Sea.