From the ABC 7 Weather team

Dense Fog: Why It Forms

August 20, 2013 - 05:15 AM
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Why does fog form?

A beautiful clear night coupled with calm winds and just enough moisture in the atmosphere equals the perfect recipe for the development of fog.  So how exactly does fog form?  Well, here's a quick explainer.

Fog is a deck of low clouds that develops very close to the surface.  Radiation fog, one of the most common types of fog, especially in our area, develops during the overnight hours when there is enough moisture present in the low levels of the atmosphere.  As the temperature drops overnight, the temperature gets closer to the dewpoint.  This means the air is becoming more saturated.  With clear skies, there is more radiative cooling at the surface promoting the development of fog. 


Radation fog generally dissipates rather quickly after sunrise.  As the sun gets higher in the sky, it warms the surface which decreases the relative humidity and helps to evaporate the water droplets that make up the low clouds and fog. 

The best advice with dense fog is to drive with extra caution and use your low-beams.  Sometimes you would think you would want to turn on your high-beams to see more, but the light reflects off the fog, which makes it much harder to see anything. 

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