One sign that winter is approaching is thick morning frost.
Frost is simply the result of saturated air.
First Alert meteorologists always emphasize that dew point is important.
In the summer, dew point reaches its highest levels of the year, and that's when people can feel moisture in the air.
But dew point is also a direct measure of the amount of moisture in the air, year-round.
At night, with a clear view of the stars, energy escapes from earth and the temperature falls.
Often times, dew point doesn't change that much while the temperatures is plummeting at night.
Since the temperature cannot fall below the dew point, water vapor in the air condenses out into liquid when the two meet.
This time of year, that occurs frequently when the air is below freezing.
Thus, instead of liquid dew, frost forms on exposed surfaces. The water vapor in the air goes directly into the solid phase, which is called deposition.
Many things can disrupt the process that leads to frost, including wind, clouds and a changing dew point.