Dense Fog Advisories (click here for graphical image from this site) and widespread IFR Conditions (click here for graphical image from this site) occurred as a nearly-occluded system spun slowly eastward across the central part of the United States on 19 March 2018. (Surface; 500-hPa). GOES-16 IFR Probability, shown above, (Click the image to see the animation) outlines two large areas where consistent IFR conditions develop/persist: the upper Plains, in states around Nebraska, and the Deep South.
The GOES-16 Night Fog Brightness Temperature Difference field (10.3 µm – 3.9 µm), animation shown below, historically has been used to identify low stratus that is assumed to be fog at night. That detection suffers when high clouds are present (consistently on the morning of 19 March over Nebraska and surrounding states; occasionally over the Deep South as convection expels high-level cirrus into the atmosphere). Because IFR Probability fuses satellite data with Numerical Model estimates of low-level saturation (from the Rapid Refresh Model), it retains a strong signal of fog in regions where multiple clouds layers prevent the satellite from observing observed low stratus causing IFR conditions, such as over Nebraska, or over Mississippi at 0607 UTC.
Note that there exists a Brightness Temperature Difference signal over the High Plains of Texas and New Mexico at, for example, 0800-0900 UTC. (See below). Persistent drought exists in that region (linked image from this site) and the dryness can alter the relative emissivities of the soils so that a signal develops (Click here for an earlier example). There are no clouds in this region; the Rapid Refresh model shows very dry air and the IFR Probability algorithm correctly diagnoses very small probabilities of IFR conditions.