Penzance does not get much real fog.

Radiation fog is rare as its on a SE facing sloped by the sea. The nearest area prone to it is around Marazion marsh.

The cloud base in typical W-SW warm sector conditions is above sea level (though often only by 50 - 100') due to the 300' high rise behind E facing Newlyn. Often the castle on St. Micheal's Mount just catches the cloud.

Banks of sea fog during warm, humid anticylonic weather rarely drift over Penzance. Even in an E-SE wind it is protected by the Lizard, so gets less fog than say Torbay which faces in a similar direction. In any case, banks of sea fog can occur at any time, and are more common in Mount's Bay in the afternoon rather than at 09:00.

As a result, the days with fog at 09:00 are low. E.g.
2013 - 9 days
2014 - 2 days
2015 - 6 days
2016 - 2 days (Bank of sea fog in June - warm sector fog in November.)

All this is leading up to the fact that I've just recorded 2 consecutive days with fog @ 09:00. Last time this happened was in 2013.

The amount of fog on the coast varies vastly from 1 spot to another. If you want to sit in fog in west Cornwall - go to Pendeen. They can have virtually a complete week of the stuff in a winter warm sector. This is something to bear in mind when forecasts say 'coastal fog patches' The distribution certainly is not random, it's very predictable from mile to mile.

Graham
Penzance