• Humidity is the amount of water vapor in the air.
  • Warm air can hold more water vapor than cool air.
  • The heat index is a measure of what the temperature feels like because of the humidity.
  • Water droplets form when the air reaches 100% humidity.
  • If the temperature is cold enough, frost will form on the surface of the grass.
  • If this temperature is below freezing, ice crystals of frost form instead of dew (Figure below).
  • The dew point occurs at 100 percent relative humidity.
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