Tonight @12:30 a.m. in Longport, NJ ( a Downbeach suburb of Atlantic City) I noticed an EXTREMELY low cloud covering the town…about level with the streetlights.
Thick cloud cover above, clear air below.
How low does a cloud have to be until it is considered fog?
Fog is often distinguished from clouds by the means of generation; fog is usually generated at or near the surface. If a stratus cloud actually got low enough to affect visibility for activities at ground level, I’d call it fog anyway.
fog has the moisture creating it coming from the earth surface.
https://www.meted.ucar.edu/training_module.php?id=795
Requires registration to access the module but you will be an expert on fog when you are finished.