Foggy Spain

Foggy Spain

The image from the OLCI sensor on Sentinel-3 satellite shows several areas of the Iberian Peninsula covered by fog.

This is what is known as  advection fog. It is formed by the movement of warmer, wetter over-oceanic air masses from the south-southeast direction over the relatively cool land surface; this usually and especially occurs in low-lying areas, mountain valleys, canyons, etc. The temperature difference between the ground and the air leaves the moisture contained in the air mass condense at low altitude, near the underlying surface.