It does not have a metaphorical meaning, only a literal meaning. In the cool mornings, fog often covers low-lying areas. After it is gone (it is said to have been "burned off" by the sun), the grass is wet. We call the moisture on the grass dew.

I would use it in my forthcoming world-famous novel. I would never speak those words in any conversation. My friends would ask, "What? You're giving the weather report?"