Frost or dew in the morning hours is formed when temperatures substantially drop at the surface as a result of heat release from the Earth into the atmosphere overnight.
When the temperature near the surface cools to the dew point temperature, saturation occurs. At that point, the suspended water droplets condense or form ice crystals on the blades of grass to form frost or dew depending on the temperature.
An old folklore states when frost or dew forms in the morning, nice weather will follow that day. Is this fact or fiction? In this case, the folklore holds true more often than not. In order for the temperature to rapidly drop to form frost or dew, clear skies, dry air, calm winds, and high pressure is generally required.
Once the sun climbs in the sky, the dry air quickly warms relative to the morning low temperature. High pressure that helped form the frost in the morning then translates to a mostly sunny day. This folklore holds strong for several hours after sunrise and generally through most of the day.
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