A photo to illustrate...
This screen shot was taken on the Norway map.
Condition set to "Poor", cloud height at 1000 meters. Date, March, 1942, 7am.
Looks pretty nice for poor weather in Norway in March I'd say. Now if the color of the sky was gray instead of blue, it would give more of a total overcast/poor weather effect, without having to add more GPU eating clouds.
Just an idea.