The weather forecast and the humidity are usually pretty good indicators. Fog is just a cloud that is on the ground. It happens because the air becomes too cool to hold the water vapor it contains, and the relative humidity goes to 100%. When that happens, the water vapor condenses on the dust that is in the air and presto! You have fog.

You didn't indicate in your profile where you live. Here in the midwestern US, weather.com is a pretty good online source for the weather forecast. They can usually predict fog a few hours in advance. YMMV.