The NWS Juneau Forecast Office issued a Dense Fog advisory valid for 9-17 UTC affecting the cities of Petersburg, Wrangell, Kake, Craig, and Klawock and areas from Dixon Entrance to Cape Decision and inner channels of this region. The MODIS and VIIRS instruments provided several passes over the region and the Night-time Microphysics RGB imagery from these NASA and JPSS instruments are shown below. At 0541Z MODIS showed a large shield of high, thick cloud (bright reds) covering extreme Southeast Alaska with a sharp edge to this cloud area through the advisory area. The Night-time Microphysics provides insight to the complex cloud structures in the area. To the north and west of this edge a mix of lower cloud features can be seen with some dull aqua coloring indicating low clouds and fog are likely and more tan colored cloud features indicating somewhat thicker low cloud. Examine the animation of MODIS and VIIRS by clicking on the image below.
Note the development of fog (dull aqua to gray coloring) near Kake and Petersburg surrounding areas and associated channels as the high, thick cloud shield moves eastward overnight. Then compare the October 15 with the animation below for the following day and note the fog development in similar areas, but also along the main coastal areas with rivers, bays, and deep valleys. Images of the individual times can be provided to those interested.