Fog and Stratus
Smooth, very low cloud sheets with warm tops called Stratus unless reaching the ground in which case they are Fog.
Fog and Stratus are seen in satellite images as low-level cloud sheets with a variable horizontal extent. Small local patches of fog are difficult to distinguish in satellite images (size in the order of a few kilometres). However, large areas of fog and stratus can cover areas over hundreds or thousands of square kilometres. Fog (or low Stratus) is formed, when moist air near ground level starts to condensate. This condensation can be produced in the atmosphere by three mechanisms: by ascent and resultant cooling of an air parcel, by radiative heat loss and by the mixing of two parcels of slightly unsaturated air initially having different temperatures. The necessary condition for both the advection and radiation St/Fog formation is a sufficient moisture content in the lowest layers of the atmosphere.