By: Meteorologist Courtney Steimann
Updated: Feb 25th 2019

Courtney's Cloud Corner: Fog

Have you ever looked up into the sky and thought how amazing it would be to be among the clouds? Well truth be told you most likely already have with surrounding fog. Fog is essentially clouds near the surface that have suspended water droplets. They can be a beautiful sight to see or a hazard for drivers, as they can reduce the visibility when on the road. Here are some types of fog you might see:


  • Radiation fog: Usually occurs in clear conditions, as this will cause the heat absorbed from the sun to escape from the surface. This will cool down the surface and cause the temperatures to align with the dew point.  When this happens the ground become saturated enough to create areas of radiation fog. Normally this would have to be seen in the wee hours of the day because it may dissipate with sun’s light.
  • Freezing fog: In this state, the temperature near the ground needs to have temperatures below freezing (32 degrees Fahrenheit). Generally, there will be supercooled liquid droplets suspended within the surface fog. When supercooled liquid droplets come in contact with any hard surface, it will tend to freeze to it.
  • Advection Fog: This type of fog can be found in windy conditions as warm air passes a cold ground. When the warm air passes, the surrounding air will gradually cool. This will create saturation and fog will occur.
  • Upslope Fog: This occurs when warm moist air is forced upward from a mountain or slope due to orographic lift. When this occurs the warm moist air is cooled and condensed creating a cloud or fog.
  • Valley Fog: Unlike the warm moist air moving uphill in Upslope fog, this fog is form when the cool dense air sinks to the bottom of a hill or mountain. As the surface releases heat that was collected from the sun, the cool air begins to sink into the valley and condense to form fog.

Now when in an area of fog, would you be able to know which type of fog it could be? 

Radiation fog shown by the buildings.
Radiation fog shown by the buildings.
Upslope fog among the mountains.
Upslope fog among the mountains.
A look at valley fog along the trees.
A look at valley fog in the downward slope.