The main reason for the difference, Ebel says, is that the California coast is right above the boundary of two of the tectonic plates that make up the Earth's crust. By contrast, Virginia is in the middle of a plate that stretches from the California coast to the middle of the Atlantic Ocean.
The radiation fog is formed when the land surface cools after the sunset in the conditions of the clear sky. Thus the cooling ground cools the air above it and as a result of this the conduction causes the air temperature to fall and hence it reaches the dew point and forms a fog.
