https://www.wunderground.com/This gives dew point and other useful info in graph form.
Condensation also depends upon the temperature of the surface water condenses on to. The classic is your glasses getting steamed up when you walk into a warm house/pub etc.. Warmer air (able to hold more moisture) hits cold glass and condenses.. So it depends on the relationship between rock temp, air temp and humidity. Mist and fog - they're different beasties... I've climbed at Almscliff in freezing fog (a few times) and conditions have been amazing, but the roads/walls were damp/wet.. crag was mint..