Fog goes up maybe a few hundred feet at most, so no. You will not see any issues. However a 5 mile thick cloud WILL have an effect on your signal. I know. I've seen it with my own eyes.
Rain, coming from a thin layer of clouds has virtually NO effect on signal. A thick thunderhead that hasn't started to precipitate yet, WILL have a noticeable effect on your signal.
Puffy white clouds? No problem with signal
Thick angry clouds? Problem with signal if it comes between your dish and the satellite, rain or no rain.