Dew point is a related incicator. The dew point is the temperature at which the air becomes fully saturated (realtive humidity rises to 100%). So if the temperature drops below the dew point then some of the water vapour will condense into droplets, giving fog. So look for days/places/times when the temperature is close to the dew point.
Also, you can expect the temperature to decrease approximately 3 F per 1000 feet of altitude (this is approximate and depends on the precise weather conditions). So if the predicted temperature is 3 F above the dew point, then on hills 1000 foot higher the temperature should have reached the dew point giving fog.
Last edited by andrew.roos; 05-12-2012 at 02:20 AM. Click to view previous post history.