Dense Fog in Anchorage

Rick Thoman writes:

Dense fog persistently blanketed parts of the Anchorage bowl for several days. At the Anchorage airport, visibility remained at two miles or less for 75 consecutive hours between Halloween and November 3rd. There were multiple smaller aircraft flights that had to be diverted to Kenai because of the low visibility. This is the second longest period of visibility remaining this low at the Anchorage Airport. The only longer streak in the past 60 years was 85 hours in mid-December 2009. The persistent fog was the result of strong high pressure remaining parked over Southcentral. The lack of wind and warmer temperatures above the fog kept the air from mixing. In fact, some of the higher elevations on the Anchorage Hillside enjoying clear skies most of the time.

LEO says:

As documented in an Alaska Dispatch News Article, persistent fog in Anchorage has impacted air travel to the city, causing flights to be diverted to Kenai. A similar observation came in from Anvik on November 1st, 2017, in which heavy fog also disrupted air travel.

Fog forms when the temperature and dew point of the air approach the same value (i.e., dew-point spread is less than 5°F) either through cooling of the air (producing advection, radiation, or upslope fog) or by adding enough moisture to raise the dew point (producing steam or frontal fog). (NOAA)

There are several types of fog: Radiation Fog forms when all solar energy exits the earth and allows the temperature to meet up with the dew point. Precipitation Fog forms when rain is falling through cold air. Advection Fog forms from surface contact of horizontal winds. Steam Fog can be seen on any lake. Upslope Fog forms as sinking air warms and rising air to cools. Freezing fog occurs with a temperature at or below freezing. When composed of ice crystals, it is called Ice Fog. This type of fog is only seen in the polar and Arctic regions. (NOAA)