I was taught advection fog can form in winds of up to 20 knots
You were indeed taught correctly, as I have been stuck on a North Sea Rig that was completely closed in with sea fog where it was indeed very blustery ~ stronger than 20Kts.
Sea Fog, or Haar?!? is indeed wierd stuff. One minute you are in bright clear warm sunshine, the next its like winter! The stuff moves around in odd patterns too, I actually enjoy watching it sometimes as the banks of fog change so quickly, spooky stuff....
Regards, SD.