A veritable buffet of things to digest are occurring in this Nighttime Microphysics RGB animation from 0600 to 1000 UTC in the early morning of 3/28/17 where multi-state impacts of stratus and fog are seen (Fig 1). In blue/aqua to gray shades, the low cloud features are developing over the central CONUS while being sandwiched between Spring-time cyclones in the East and West. The massive spreading of the stratus and fog can’t be missed and numerous METAR observations across the central CONUS verified the aviation hazards.
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Focusing on the Tennessee and Lower Mississippi Valley regions, the fast motion of the animation from 0900 to 1130 UTC allows one to see the development of fog while other stratus clouds pass to the east/northeast (Fig 2.). Note that fog develops in the various low-lying areas, particularly eastern Tennessee valleys. There is also a separate push of fog, noted by the black dotted oval of Figure 3, that moves southward along the back side of the eastern cyclone. The METAR stations in the oval show the lowest visibility observations occurring in this area of southern and western Tennessee as well as northern Alabama. A bit further upstream (north) from the push of fog there is a layer of very low stratus also moving southward and causing MFVR to IFR conditions. With the large amount of precipitation from the previous day and relatively light winds overnight, a variety of fog and stratus developed over a wide area as the cyclone passed. While not extremely common there are instances where fog develops even with low stratus present overhead. One can see this in central Missouri where fog is reported but the RGB shows stratus with large water droplets at their tops. Fog below stratus was experienced at times in northern Alabama as well.