Usage patterns
霧が出るfor fog to form/appear
Fog rolled in this morning and visibility was poor.
霧が晴れるfor fog to clear/lift
By noon the fog had cleared and the mountain came into view.
霧がかかるfor fog to hang over/settle on (a place)
A thick fog hung over the lake.
濃い霧thick/dense fog
The flight was cancelled due to thick fog.
Expressions
黒い霧black fog; veil of secrecy; cover-up 霧に包まれるbe shrouded in mist; be enveloped in fog 霧に覆われるbe shrouded in mist; be enveloped in fog