Sunrise Offers Beautiful View Of Dense Valley Fog

 

Sunrise on Sunday morning offered a beautiful view of dense valley fog, if you happened to be on a ridge top. High pressure at the surface and aloft allowed for an atmospheric setup that promoted sinking air. This sinking air helped to suppress what little moisture that was in the atmosphere into the valleys. Overnight, clear skies and calm winds helped valley temperatures quickly fall to their dew point. Once the temperatures reached the dew point, the air was saturated and fog was able to form. Meanwhile, the ridge tops stayed much warmer because they stayed "connected" to the upper level winds. This created a temperature "inversion" in which warm air at the ridge top level sat over the top of cooler air in the valleys. The end result was valleys, especially river valleys, filled with fog and ridge tops sticking above the fog under clear skies. Below are several images from Sunday October 25th, around sunrise.

The image above is a visible satellite view of eastern Kentucky around sunrise on Sunday morning. Notice the white (fog) taking the shape of valleys across much of extreme southeast Kentucky.

The image above is a picture taken from the ridge top at the Jackson Julian Carroll Airport in Breathitt County about the same time as the satellite image above. You are looking southeast toward the Kentucky and Virginia borders. Notice how the fog is suppressed in the valleys and ridges are sticking out above the fog. Imagine the inversion that was talked about above in between the fog in the valleys and the ridges above. The elevation at the airport is 1,357 feet above seal level. The relief from the top of this ridge to the valley floor is roughly 600 feet.

Above is a picture taken about a half an hour later from roughly the same spot. Notice how the fog has begun to rise out of the valleys and start to obscure the ridge top. What is happening? The sun has risen higher in the sky at this point and some very interesting meteorological phenomenon have started to take place. As the sun gets higher in the sky the temperature begins to rise, and as a result, the air itself begins to rise. The rising temperatures in the valleys begin to equal the higher temperature of the ridges, and the "inversion" mentioned above begins to disappear, allowing the fog (now low stratus) to rise higher. This process helps to lift the fog out of the valleys like you are seeing in the image above. Another interesting process is also occurring with regard to the amount of moisture in the air. As the temperature rises, it moves further away from the dew point. Once this happens, the air is no longer saturated and drier air begins to "mix" the fog out. Eventually the fog completely dissipates, or if there was enough moisture, turns into low stratus or low cumulus clouds by mid morning. In most cases, the thicker the fog the longer it will take to "mix" out. However, many other meteorological factors also play into this such as mid level sky cover, wind speed, and wind direction.



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