|WHAT CAUSES DEW AND FROST?
METEOROLOGIST JEFF HABY
Dew is liquid moisture on the ground that is seen in the morning. It can be confused with rain but the moisture
did not result from rain. At night the ground will cool. If there is enough moisture in the air and the
cooling is great enough then condensation will occur on the ground. The formation of the condensation is the
same process that occurs when you leave a glass of ice water out when there is moisture in the air. You will
see condensation forming on the outside of the glass. This is because the glass is cold (ground is cold) and
there is enough moisture in the air that the dewpoint is reached. Vegetation and animals can get moisture from
the dew forming process even when there is no moisture available from rain.
Frost forms is the same way as dew except it occurs when the dewpoint is below freezing. True frost forms
when the temperature is below freezing. The moisture goes straight from a gas to a solid. If the
moisture goes from a gas to a liquid and then to a solid then the result will be frozen dew. You can tell
the difference between frost and frozen dew by looking at them. Frost looks more feathery, brighter and you
can see the crystal formations. Frozen dew is solid and does not have quite the white appearance
Next time you see dew, frost or frozen dew think about the process that formed it.