In the image above, a trough of low pressure is depicted along the Mississippi River, with moist southerly flow over the Ohio Valley and Western Great Lakes (Dewpoints in Wisconsin at this time were mid- to upper-40s (Fahrenheit). This moist air is easily cooled to its dewpoint by the underlying cool ground, and dense fog is a result. However, this fog is difficult to detect from satellite because of the multiple cloud layers that accompany low pressure systems. GOES-R IFR Probabilities show a good signal because of Fog Predictors that are derived from numerical model output (the numerical model used is the Rapid Refresh). In this case, the Rapid Refresh was accurately depicting the evolution of the system because the model-based field of IFR Probabilities accurately overlaps the region of observed IFR (and near-IFR) conditions.