Fog in the river and mountain valleys of Pennsylvania and New York on Aug. 20, 2013. Image credit: SSEC/NOAA
Spreading like veins on the earth's surface, fog can be a spectacular sight from space.
Specifically, we're talking about river and mountain valley fog. The slideshow above and the animation below illustrate the unique views that valley fog produces from above.
(MORE: How Does Fog Form?)
Mountain valley fog is just a type of radiation fog.
Radiation fog forms at night when winds are light, skies are clear and there is moist air near the surface of the earth. As the air cools at the surface, it becomes saturated, leading to the formation of fog.
In mountain locations, air from elevated areas near mountain valleys cools and becomes more dense and heavy. As a result, the cold air drains into the valleys below where it continues to cool and the radiation fog forms.
River valleys are also prone to the formation of radiation fog. However, sometimes the fog found over rivers, streams and lakes is caused by steam fog.
Steam fog forms when cool air moves over and mixes with the relatively warm and moist air near the surface of the water. The moist air then cools and becomes saturated, causing fog to form.
At times, fog in river valleys can be from a combination of radiation fog and steam fog.
River Valley Fog Animation
Satellite loop of fog dissipating in the river valleys of southern New York and northern Pennsylvania on Aug. 20, 2013. Credit: NOAA/SSEC