I do a lot of night hunting for varmits. Sometimes if it has rained the previous day I will get fog that evening. Although rain is not nessary for fog in my medow it seems to come and go as it pleases with the evening temp only having to drop a few degrees. It may appear many different times in a evening/night for no apparent reason, though I am sure there is one. As this is an hour drive from my home I would like to predict whether or not it would be a clear evening. Oh and sometimes there will not be fog anywhere else in that 1 hour drive. Seems to create its own weather, can you help??

Warm air can hold more moisture than cold air, when warm moist air hits cool air, it can't hold the moisture and "Drops" as rain or fog.
You need a way to measure dewpoint, when dewpoint and temperature are close fog will form.
What is dewpoint temperature?

Fog - Wikipedia, the free encyclopedia