There are different ways to alert a forecaster to the presence of a transporation hazard like low ceilings and reduced visibilities. The imagery above shows GOES-based (nominal 4-km resolution at nadir) products (top) and Suomi/NPP and MODIS-based products (nominal 1-km resolution — or better — at nadir). The Brightness Temperature Difference from GOES (upper right) overestimates the region with lowered ceilings; in contrast, the IFR Probability field (upper Left) is able to distinguish between elevated stratus and low stratus because it includes information from the Rapid Refresh model to identify regions with saturation in the lowest levels of the atmosphere. This allows the IFR Probability to screen out regions of mid-level stratus.
The Suomi NPP and MODIS Brightness Temperature Difference fields do not suggest widespread stratus as does the GOES-based Brightness Temperature Difference field. Rather, the data from the polar orbiters suggest regions of stratus or fog in river valleys over Kentucky, Indiana and Illinois. MODIS-based IFR Probability (Lower Right) agrees with the GOES-based IFR Probability field: a region of fog/low stratus is developing over southwestern Indiana and southeastern Illinois, near the Wabash River. In this case, the model data is helping to strengthen a weak signal in a region where fog is present. Model data is a key strength in the IFR Probability field.
Polar orbiters give excellent horizontal resolution, but only GOES provides the high temporal resolution necessary to monitor the development of fog/low stratus. The toggle between 0800 and 1100 UTC, below, for example, depicts an increase in fog. A single GOES satellite can (and does) monitor that increase. A suite of polar orbiters would be required to give similar temporal coverage in middle latitudes.