Short answers, pulled from the story.
Fog forms when the difference between air temperature and dew point falls below 2.5 degrees Celsius, causing water vapor to condense into tiny droplets suspended in the air. The droplets collect on condensation nuclei such as dust, ice, or salt particles. Fog is defined as any such condition that reduces visibility to less than one kilometer.
Fog reduces visibility to less than one kilometer, while mist causes lesser impairment of visibility. Fog is also less transparent than mist.
Pogonip is a type of freezing fog that occurs in the western United States, particularly in deep mountain valleys during cold winter spells. The word comes from the Shoshone word paγi̵nappi̵h, meaning "cloud". The Columbia Plateau experiences pogonip most years during temperature inversions, sometimes lasting as long as three weeks, with fog spreading as far south as La Pine, Oregon, almost 150 miles from the Columbia River.
The Grand Banks of Newfoundland are widely considered one of the foggiest places in the world, with an average of 200 or more days in fog each year. This is caused by the meeting of the cold Labrador Current from the north with the warmer Gulf Stream from the south.
During D-Day on the 6th of June 1944, Allied forces landed on the beaches of Normandy under fog conditions, with both positive and negative results reported from both sides due to impaired visibility. The British also developed Fog Investigation and Dispersal Operation (FIDO), which burned large amounts of fuel alongside runways to evaporate fog and allow returning fighter and bomber pilots to land safely.
Low-pitched sounds have long wavelengths that move air slowly and lose little energy to interactions with fog's tiny water droplets. High-pitched sounds have short wavelengths that are reflected and refracted by those droplets, dissipating their energy through a process called damping. Low-pitched tones therefore travel farther through fog.