Patchy fog possible again tomorrow morning: Here are some different types of fog and how each one forms

Visibility reduced by several miles during the morning commute

Patchy fog possible again tomorrow morning: Here are some different types of fog and how each one forms
Visibility Futurecast (Source: WWSB)


It was another foggy Wednesday morning for some of us across the Florida Peninsula with dewpoints in the 70s and calm winds. Dew points and the air temperature is expected to be in the low 70s and winds will be light. As a result, Radiation Fog, also known as Ground Fog, is likely to occur for parts of the Suncoast once again early Thursday morning.

What is the Dew Point?

It’s the temperature at which the air mass needs to reach in order to become saturated. In other words, dew point is a measure of the amount of moisture in the atmosphere. The air temperature can never be lower than the dew point. One way to bring the air temperature down to the dew point temperature is through a cooling process.

Visibility Futurecast
Visibility Futurecast (Source: WWSB)

Forms of Fog

Radiation Fog (Ground Fog): This fog forms when all solar energy exits the earth and allows the temperature to meet up with the dew point. The best condition to have radiation fog is when it had rained the previous night. This help to moisten up the soil and create higher dew points. This makes it easier for the air to become saturated and form fog. However, the winds must be light less than 15 mph to prevent moist and dry air from mixing.

Precipitation Fog: This is fog that forms when rain is falling through cold air. This is common with a warm fronts but it can occur with cold fronts as well only if it’s not moving too fast. Cold air, dry at the surface while rain is falling through it evaporates and causes the dew point to rise. This saturation forms fog.

Advection Fog: This type of fog forms from surface contact of horizontal winds. This fog can occur with windy conditions. Warm air, moist air blows in from the south and if there is snow or cool moisture on the ground it will come in contact with the warm, moist winds. This contact between the air and ground will cause the air blowing in to become cool. Then dew point rises and creates high humidity and forms fog.

This type of fog is also known as Sea Fog and can form at a moment’s notice, leading to near zero visibility. It occurs most often during Florida’s winter and spring months when the water temperatures are the coolest. It has been responsible for several ship wrecks and incidents over the years.

Steam Fog: This type of fog is commonly seen in the Great Lakes but can be seen on any lake. This forms during the fall season. As summer ends, water temperatures don’t cool right away but air temperature does. As a mass of dry, cold air moves over a warmer lake the warm lake conducts warm, moist air into the air mass above. This transport between the lake and air evens out. This corresponds to the second law of thermodynamics and this law state “any two bodies that come into contact, the system will become equilibrium state.” Steam fog does not become very deep but enough to block some of the sunlight.

Upslope Fog: This fog forms adiabatically. Adiabatically is the process that causes sinking air to warm and rising air to cool. As moist winds blow toward a mountain, it up glides and this causes the air to rise and cool. The cooling of the air from rising causes to meet up with the dew point temperature. Fog forms on top of the mountains.

Valley Fog: Valley fog forms in the valley when the soil is moist from previous rainfall. As the skies clear solar energy exits earth and allow the temperature to cool near or at the dew point. This form deep fog, so dense it’s sometimes called tule fog.

Freezing Fog: Freezing fog occurs when the temperature falls at 32°F (0°C) or below. This fog produces drizzle and these tiny droplets freeze when they come into contact with an object. But at the same time there is sublimation going on.

Ice Fog: This type of fog is only seen in the polar and artic regions. Temperatures at 14 F (-10°C) is too cold for the air to contain super-cooled water droplets so it forms small tiny ice crystals.

Tips for driving in fog

  • Minimize distractions
    • Silence your cell phone and the stereo. Put distractions like your cell phone in a place where you won’t be tempted to reach for them while driving, like the glove compartment.
  • Reduce your speed
    • Because you can’t see the road or other vehicles, a low speed can help you react safely.
  • Roll down your window
    • This allows you to listen for cars and emergency vehicles.
  • Use roadside reflectors as a guide
    • The markings can help you navigate twists and turns.
  • Turn off cruise control
    • This will maximize your control of your vehicle.
  • Use windshield wipers and defrosters
    • Limits excess moisture on the window and reduce glare.
  • Drive with low beams and fog lights
    • High beams can worsen visibility because they reflect off the fog.
  • Use the right edge of the road as a guide
    • Helps you stay in your lane and not “drift” into the middle lane.
  • Increase your following distance from other cars to ensure you have the proper time to respond to any obstacles
    • A good rule of thumb is to increase your count distance by at least 5 seconds instead of the normal 2 seconds behind another vehicle.
  • Beware of animals on the road
    • Animals, especially white tail deer, feel bolder under cover of fog and are much harder to see. The lowered visibility in dense fog means less time for you to see them, and for them to see you.

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