File:Multi-layer clouds over the southeastern United States (MODIS 2016-12-27).jpg

English: A stalled cold front brought cold weather and a complicated cloud pattern to the southeastern United States in late December 2016. The Moderate Resolution Imaging Spectroradiometer (MODIS) aboard NASA’s Terra satellite captured a true-color image showing multi-layer clouds on December 20.

Low clouds (fog) hang in the Tennessee Valley, with the fog bank stretching from the northeast to the southwest, then turning southward. A higher layer of cloud extends from the west to the east and joins the frontal system which lies roughly over the coast.

The Appalachian Climate Center reported that a warm layer aloft was generating a strong inversion, trapping lower clouds beneath it. The fog was said to be primarily orographically generated, meaning that it was formed as moist air rose upward and became saturated. Weather advisories for much of the northern Tennessee Valley warned of thick, freezing fog. Riming – the formation of a layer of tiny, white, granular ice particles – caused by the rapid freezing of supercooled water droplets when they impact an object.

Forecasts in parts of Tennessee, eastern Alabama, and other parts of the southwest called for rain, or freezing rain in addition to fog. The higher-level clouds were responsible for the precipitation.