Kotsch - Weather for the Mariner - Fog

Question 1

Fog - results from…

Answer 1

• cooling air that remains at earth’s surface

Question 2

Fog - Dew Point is…

Answer 2

• temperature a given parcel of air must be cooled for saturation to occur
• at constant pressure and water vapor content

Question 3

Fog - Dew point spread is…

Answer 3

• difference between air temperature and dew point
• fog is imminent as spread approaches zero

Question 4

Fog - dew point of maritime air masses are…

Answer 4

• higher than land air masses

Question 5

Fog - dew point - higher vs. lower temperature changes

Answer 5

• small rise in higher temperatures allows for much more water vapor accommodation than same rise in lower temperatures
• takes longer to dissipate fog in winter than summer

Question 6

Fog - Radiation fog is favorable during…

Answer 6

• autumn and winter

Question 7

Fog - Radiation fog occurs with these factors present…

Answer 7

• nightime
• land based
• clear sky
• light wind, ﹤15 kts
• high relative humidity at sunset

Question 8

Fog - Radiation fog occurs when…

Answer 8

• small decrease in night temperature reaches dew point

Question 9

Fog - Radiation fog is land based because…

Answer 9

• heating qualities of water
• water surfaces day/night temperature change is ≤ 3℉

Question 10

Fog - Radiation fog collects…

Answer 10

• in valley bottoms and shorelines where the cool air drains to

Question 11

Fog - Radiation fog usually dissipates…

Answer 11

• 1-3 hours after sunrise

Question 12

Fog - Advection fog occurs when…

Answer 12

• day or night
• warmer air blows over colder surface (land or water) cooling the air to the dew point
• the cooling air becomes more stable and does not rise

Question 13

Fog - Advection fog over the sea with wind

Answer 13

• still forms with wind ≤ 30 kts due to less friction over the water

Question 14

Fog - Advection fog - reasons for colder water surface

Answer 14

• cold water current (ie. Labrador Current)
• cold upwelling of water (ie. off northern California coast)
• contrasting water temps (ie. Bering Sea colder than North Pacific along Aleutians)
• river drainage of colder fresh water (less dense) into relatively warm salt water (ie. northern Gulf of Mexico in winter)

Question 15

Fog - Tropical-Air fog is…

Answer 15

• advection fog from the gradual cooling of air as it travels to higher latitudes

Question 16

Fog - Tropical-Air fog commonality

Answer 16

• more common over water with less friction
• most common type of fog over open sea
• most widespread fog observed in US

Question 16

Fog - Frontal fog is…

Answer 16

• rain from warm air above falls to colder air below
• evaporation of the warm rain raises dew point of colder air

Question 17

Fog - Frontal fog is found…

Answer 17

• sometimes ahead of warm and occluded fronts, and behind cold fronts

Question 18

Fog - Inversion fog is typically found…

Answer 18

• in subtropical west coasts of continents (ie. California)

Question 19

Fog - Inversion fog occurs when…

Answer 19

• wind action over cold upwelling water gives air lower temperature and high relative humidity
• offshore fog forms similar to advection process and works its way inland at night as the land cools

Question 20

Fog - Inversion fog - inversion created

Answer 20

• higher temperature air above creates “lid” preventing the cool moist air from rising

Question 21

Fog Over the Sea - trade wind belts

Answer 21

• Sea fog is rare except along coasts of California

Question 22

Fog Over the Sea - middle to high latitudes

Answer 22

• common, esp. in spring and summer

Question 23

Fog Over the Sea - spring/summer general occurrence

Answer 23

• warm/moist air from land to sea produces fog over coastal waters
• wind shift tends to bring that fog back onto land

Question 24

Fog Over the Sea - fall/early winter general occurrence

Answer 24

• air from sea to land produces fog in coastal areas
• wind shift may drift to sea