Fog on Delmarva

There are many types of fog and they get their name from how they form.  To name a few, there is advection fog, radiation fog, steam fog, upslope fog, precipitation fog, and valley fog.  The two that affect us on Delmarva are the advection and radiation fog.  With advection fog a warm and humid air mass moves in over cool ground.  The cool ground helps to drop the temperature of the warm air mass to the dew point which increases the humidity to 100 percent and a cloud forms, also known as fog.

Radiation fog is slightly different and it’s what we’ve seen that past few mornings.  With clear skies, radiation from the sun heats the earth, but once the sun goes down that heat escapes back into the atmosphere.  This cools the lowest levels of the atmosphere to the dew point for complete saturation.  The water molecules form small water droplets reducing visibilities.  Fog forms at the surface and continues to build up as long as the air can be cooled to the dew point.  This type of fog gets thicker and thicker as the night goes on. 

One thing that will inhibit fog is wind, so if the wind picks up, the air will begin to mix through the entire lower level of the atmosphere, slightly dropping humidity values and the fog will dissipate.