Brightness temperature Difference field (10.7µm – 3.9µm) from GOES East over the southern Plains, 1000 UTC on 6 April 2015 (Click to enlarge)

The heritage, traditional method for detecting fog and low stratus is the brightness temperature difference product, seen above (with an enhancement) at 1000 UTC on 6 April. It is difficult to discern a difference in the field over regions where IFR conditions are reported versus regions where IFR conditions are absent. In contrast, the IFR Probability Field from the same time, below, neatly outlines the regions of IFR conditions, and, importantly, does not highlight regions — such as Fort Smith AR and Poteau, OK — where IFR conditions are not present.

GOES-R IFR Probability Fields, 1000 UTC on 6 April 2015 UTC (Click to enlarge)