Valley Fog Near Oswego, New York

February 08, 2008

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Provided by:
Mark Muller, Gilbertsville-Mount Upton Central School District
Summary authors & editors: Jim Foster, Mark Muller 

The photo above shows fog gripping a stream valley near Oswego, New York. It was taken early in the morning on September 19, 2007. Clear skies during the preceding night enabled the ground to cool (radiation cooling), which resulted in a net loss of heat. Radiation fog, also known as ground fog or valley fog, commonly occurs in late September and October. When nights are longer than days, there is more time for the surface to cool to a temperature at or below its dew point. If the landscape is gouged a bit, fog will cling to the low-lying areas as long as the air there remains saturated. Note that the fog is absent from surfaces that are more elevated. As the air heats up and dries later in the morning, the fog then evaporates.

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