What is Fog?

By: Tracey Anthony
By: Tracey Anthony

Lately on Daybreak there have been quite a few mornings you hear me warn viewers about fog. Fog can be a major weather hazard especially when out on the road.....So what is fog?

Lately on Daybreak there have been quite a few mornings where I am warning viewers about fog. Fog can be a major weather hazard especially when out on the road. 

So what is fog? 
Fog is no different than some of the clouds you see in the sky. In fact, fog is defined as a type of stratus cloud that forms near the ground. Fog begins to form when water vapor condenses into tiny liquid water droplets in the air. Water vapor tends to condense on condensation nuclei such as dust, ice, and salt in order to form clouds. 
Photo Credit: National Weather Service
Read More: http://www.crh.noaa.gov/jkl/?n=fog_types
Types of Fog include, radiation fog, advection fog, upslope fog, freezing fog, ice fog, and evaporation/mixing fog. 
Here in the Mid-Ohio Valley we tend to see radiation (valley fog) or advection fog. Both types of fog are formed by condensation. Think of this like an iced beverage you take outside on a hot summer day. Condensation forms on the outside of the glass. That is the warm outdoor air touching the glass being cooled to its saturation point.
Radiation fog usually occurs on a mostly clear night when the earths surface emits heat that is lost into the atmosphere. The air  temperature above the ground will then start to cool. Once the air has cooled down near the dew point (relative humidity close to 100%) the air condenses into water droplets and fog will form. 
Advection fog occurs when a warm moist air mass passes over a colder surface and is cooled.  You see this when fog is formed as warm air moves over water ways or warmer air moving horizontally over snow. 
Did you know? Some cities around the world rely on what is called a "fog catcher" for daily water needs. 
"The village of Bellavista, Peru, relies on fog catchers. Bellavista is an area that has little access to liquid water—no rivers, lakes, or glaciers are nearby. Wells dry up quickly.  Water for irrigation and human consumption is threatened. Every year, however, huge fogs blow in from the Pacific Ocean. In 2006, the community invested in a series of fog catchers outside of town. Now, the residents of Bellavista have enough water to irrigate trees and gardens, as well as provide for their own drinking and hygiene needs."
Photo Credit: National Geographic
Read More: http://education.nationalgeographic.com/education/encyclopedia/fog/ar_a=1#page=1
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