A fast-moving clipper system brought a mix of sleet, snow, freezing rain, then rain to the Huntsville county warning area on Groundhog Day. Much of the area quickly cleared out this evening, resulting in widespread fog formation–and temperatures falling to around freezing.
This is a dynamic fog event, however; fog at an aviation forecast site in northwest Alabama, Muscle Shoals (KMSL) dissipated somewhat since the late evening hours (visibility improved from 3/4 mile to 7 miles in a half-hour), while fog is expanding in southern Tennessee due to eroding clouds.
The MODIS pass from 0340 UTC shows the extent of the fog (yellowish-white color) in the late evening hours, as well as the bank of clouds (yellowish-orange) across middle Tennessee. You can also see terrain influences, such as the narrow Big Wills Valley in extreme northeast Alabama (where numerous bridges are reported to be icy) and northwest Georgia.
Compared with the 0752 UTC pass, the fog is much more widespread–but still indicates that it is not as widespread as previously expected over northwest Alabama. The expansion of fog in southern Tennessee is also apparent.
MODIS imagery can’t catch everything, however–visibility has decreased again at Muscle Shoals, perhaps due to the mesoscale effects of the nearby Tennessee River.