The MODIS sensor aboard the Aqua Satellite captured the development of narrow valley fog along the Tennessee River in the Great Valley of East Tennessee yesterday morning as seen in Figure 1 below. The fog appears as the narrow area of yellow color stretching from KTYS (McGhee-Tyson Airport – Knoxville) westward, then southwestward to KCHA (Chattanooga, TN). The other colors represent terrain (purple shading represents the valley floor while the greens – yellows – reds – browns -whites represent the higher terrain to the east and west).
The fog follows the course of the Tennessee River as it winds southwestward from Knoxville to Chattanooga. At this time, Knoxville was only reporting visibility of 6 statute miles while shallow fog (fog less than 6 ft deep) was reported at the Chattanooga airport. Nevertheless, the higher resolution MODIS instrument was able to detect the early development of the fog along the Tennessee River channel, while also indicating that the fog was not a widespread event in the Tennessee Valley. With only two sensors reporting visibility in the area, an operational forecaster might have had to make assumptions about the extent of the fog, barring any other timely reports.
Notice in the two last figures, which are GOES images, taken just before and after the MODIS image around 0800Z and 0830Z, the fog does not appear nearly as well.