Meteorological parameters, such as surface pressure, geopotential height at 500 hPa and relative humidity at 700 hPa, give us information on whether the synoptic conditions are favorable for fog formation. The following animations display satellite images in combination with outputs from numerical models.
In the following animation we can notice a non-gradient field of pressure, which causes calm weather conditions. The pink lines represent the field of geopotential height at 1000 hPa, and the blue ones at 500 hPa.
Anim. 4.1. Surface pressure and geopotential height at 500hPa
In the middle troposphere the air is relatively dry, which enables radiation cooling of the boundary layer.
Anim. 4.2. Relative humidity at 700hPa
We can see that the satellite image RGB combinations, as well as basic meteorological fields, show a typical synoptic background for a radiation fog formation.
To better understand the boundary layer conditions during the fog event, we will also consider a parameter called dew point depression (difference between the surface temperature and dew point temperature).
Anim. 4.3. Dew point depression