What is frozen dew and how does it form? Frozen dew is simply frozen water that forms on objects during a clear, calm, and cold night. Frozen dew forms when the air temperature near the ground reaches the dew point, while the dew point is above freezing. Remember, the dew point is the temperature at which water condenses.
White frost or hoar frost forms during a clear, calm and cold night. The difference between frost and frozen dew is this: the dew point is at or below freezing. When the air temperature continues to cool to and below the freezing dew points, water vapor can change directly to ice. This gives frost a white color. Another distinguishing feature is that frost tends to look like a branch, if you looked at it closely.
If we were to measure the temperature a couple feet off the ground we might find that the temperature is above freezing, yet frost has formed. This occurs because the temperature right at the ground level is at the freezing mark. This is why we can have temperatures in the upper 30s and still have frost on the ground.