Dew forms on grass in the early morning because of condensation, which happens when the temperature of the grass (or other surfaces close to the ground) cools down overnight to the dew point temperature—the temperature at which the air becomes saturated with moisture and can no longer hold all the water vapor it contains. As the grass cools by radiating heat, water vapor in the air condenses into liquid water droplets on the cooler surface. This process is most common on clear, calm nights following warm, sunny days, and depends on factors like humidity, temperature, and dew point.
Why Dew Forms on Grass
- Grass and other surfaces close to the ground cool quickly by radiating heat into the open sky at night.
- When they cool to the dew point, the moisture in the air condenses as water droplets on these surfaces.
- Dew forms more readily on clear nights because clouds can trap heat and keep the ground warmer, preventing condensation.
Dew Point and Moisture
- Dew point is the critical temperature where air becomes saturated (100% humidity) and water vapor turns to liquid.
- Humidity and soil moisture affect dew formation; wetter soil and higher humidity increase dew likelihood.
- If temperatures drop below freezing, dew can freeze into frost instead.
Common Conditions for Dew
- Clear skies at night to allow ground cooling.
- Calm or light wind conditions.
- A previous day with warmth to provide moisture in the air.
- Ample moisture available in the air or soil.
Thus, early morning dew on grass is basically moisture from the air that condenses due to nightly cooling of the grass surface reaching or dropping below the dew point temperature.
