|About Dense Fog and Smoke
The main period for fog formation in South Florida is from late Fall to early Spring. When fog does form in South Florida, it typically forms over the Evergldes and along the southwest coast of Florida. The western suburbs of the metropolitan areas from West Palm Beach to Miami can also see fog at times. However, fog in uncommon along the south coast of Florida.
Wildfires, as well as controlled burning for agricultural and land management purposes, can produce large areas of smoke over the rural interior of South Florida. This occurs primarily during the drier months from November to May. While most of the burning occurs in remote areas and has little impact on the population, there are rare occasions when smoke pushes close to roads or developed areas.
Fog or smoke are considered dense when the visibility is lowered to a quarter of a mile or less. The combination of smoke and fog is a very dangerous situation that can lower visiblity to zero. If dense fog is predicted or observed over a large enough area, the National Weather Service wil issue a Dense Fog Advisory. For marine interests, the potential for dense fog will mentioned in the Coastal Waters Forecast, and in Marine Weather Statements as needed.
For the purposes of the daily Hazardous Warning, the five-tiered Levels of Concern are described below. The color system shows coverage of dense fog or smoke (1/4 mile or less) over an area.
Causes of fog formation over South Florida
The Earth constantly radiates infrared energy into the atmosphere. On nights when there is little cloud cover to absorb and scatter this energy, it radiatiates into space. This is called radiational cooling, since it tends to cool the ground in the process. The cooling ground in turn cools the ground immediatly above it. Given sufficient low level moisture, this allows the water vapor in the air close to the ground to condense into tiny cloud droplets. In other words, the water vapor (an invisible gas), cools and turns into a mist of suspended drops of water (fog). This is the main mechanism for fog formation in South Florida. Winds tend to disrupt this process by allowing the cooling moist air near the ground to mix with warmer and often drier aloft. This type of fog is classified as radiational fog.
The second mechanism for fog production in South Florida is advection fog. "Advection" is what meteorologists call the movement of air along a surface. Advection fog occurs when warm. moist air off the Gulf of Mexico or the Atlantic moves (or "advects") over a cooler land surface. This happens occasionally during the Spring when maritime air is gradually warming, but air over the land is still influenced by periodic cold fronts. As with radiation fog, the cooling moist water vapor condenses into fog. This is often responsible for fog formation over the southwest coast of Florida. Sometimes fog is formed by a combination of both processes.
Dense Fog or Smoke Safety Rules