West & north facinc coasts of Cornwall are being troubled by a large bank of sea fog. I think recent satellite images are interesting, here's a recent typical one.
I suspect the clear slot off the north coast is at least partly due to the seaward descending edge of the sea breeze circulation. The sea breeze rising up the cliffs helps the mist to reform just behind the beach.
I have researched this thoroughly by spending time on a west facing beach & staring out to sea. It is most apparent with approaching thin, semi transparent Sc, which dissipates completely 2 or 3 miles off shore, to be replaced by small Cu just inland of the beach.
Sunny in Penzance, but with the sea fog so close, the temperature is being held back to near 21C currently. Some gusty conditions along the edge of the sea fog, as is typical.