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Weather IQ: How Fog Forms

Fog is a common weather phenomenon which can be hazard to start off the day. Here is how it forms and some of the different types.


What is Fog:

Fog is simply a cloud that touches the ground. Where depending on several factors can lower visibilities down to zero making it nearly impossible to see in front of you. 

Interesting Fact: Fog droplets are extremely fine where you can fit 1 billion fog droplets into a team spoon.

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Fog Ingredients:

  1. A wet ground where water evaporates into water vapor and then condenses into fog. 
  2. A clear sky. A clear sky allows the temps to maximize their cool down which enables a the atmosphere to become completely saturated. Or max out relative humidity.  
  3. Calm winds. A strong breeze will break up fog. It needs a calm wind or light air to allow it to build in place.  

The most common type of Fog is Radiational fog an is what we commonly see in the Charlotte area.

Typical Set Up: Overnight, the heating from the day radiates upward and when you have a moist surface, water evaporates into water vapor and condenses. Clear skies allow this process to happen freely and most effectively. When winds are calm, the fog just sits there. And when winds pick up it can disperse fog.

Other Types of Fog:

Advection Fog: Advection means the transport of air horizontally. When warm moist air rides over a cool surface, fog is formed. This fog is most common on the Pacific Coast.  

This is the fog you see around the golden state bridge.

Valley fog: this is appropriately named and happens usually during winter. When the Mountains cap the airs lift fog gets trapped in the lower elevations or the valley. 

Freezing fog: this is when simply the fog droplets form and freeze onto solid surfaces. The National Weather Service will issue a Freezing Fog Advisory if this happens. 

Fog's Worst Enemy:

And lastly, fogs worst enemy is the sun. Fog is usually gone by the afternoon because the sun warms it in the morning, causing it to rise and then dissipate. 

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