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The Science Behind: Fog, Mist & Haze

Radiation fog is most prevalent during the fall and winter

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JACKSONVILLE, Fla. – Foggy mornings are synonymous with autumn as the changing foliage. The fact is many mornings over the past couple months and through the rest of this month, we’ll experience a foggy start to the day. 

You may not be aware of this, but there are different types of fog – mountain/valley fog, super fog, freezing fog, advection fog, and radiation fog.   

According to the National Weather Service, radiation fog is a very common type of fog throughout the United States and it’s also the most common visibility deterrent across Northeastern Florida and Southeastern Georgia.  

Radiation fog is most prevalent during the fall and winter. It forms overnight as the air near the ground cools and stabilizes. When this cooling causes the air to reach saturation, fog will form. Fog will first form at or near the surface, thickening as the air continues to cool. The layer of fog will also deepen overnight as the air above the initial fog layer also cools. As this air cools, the fog will extend upward. 

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The most favored areas for fog development are sheltered valleys where there is little to no wind and locations near bodies of water. Wind would disrupt the formation of radiation fog. Radiation fog is usually patchy, tends to stay in one place and goes away the next day under the sun’s rays.Thicker instances of radiation fog tend to form in valleys or over calm bodies of water.

While we mostly talk about fog, many time terms we use to describe poor visibilities can be confusing. 

Fog: Fog is water droplets suspended in the air at the Earth's surface. Fog is often hazardous when the visibility is reduced to ¼ mile or less.

Mist: A visible aggregate of minute water particles suspended in the atmosphere that reduces visibility to less than 7 statute miles, but greater than or equal to 5/8 statute miles. It does not reduce visibility as much as fog and is often confused with drizzle.

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Haze: An aggregation in the atmosphere of very fine, widely dispersed, solid or liquid particles, or both, giving the air an opalescent appearance that subdues colors.

When foggy conditions are expected or are prevalent across the area the NWS will issue a Dense Fog Advisory. When this happens, visibilities frequently drop to one-quarter of a mile or less. These conditions make travel difficult. Take extra caution when on the road or avoid driving if possible.

The NWS suggest that you keep these tips in mind if you must drive in foggy conditions:
If you must drive in foggy conditions, keep the following safety tips in mind:

  • Slow down and allow extra time to reach your destination.
  • Make your vehicle visible to others both ahead of you and behind you by using your low-beam headlights since this means your taillights will also be on. Use fog lights if you have them.Never use your high-beam lights. Using high beam lights causes glare, making it more difficult for you to see what’s ahead of you on the road.
  • Leave plenty of distance between you and the vehicle in front of you to account for sudden stops or changes in the traffic pattern.
  • To ensure you are staying in the proper lane, follow the lines on the road with your eyes.
  • In extremely dense fog where visibility is near zero, the best course of action is to first turn on your hazard lights, then simply pull into a safe location such as a parking lot of a local business and stop.
  • If there is no parking lot or driveway to pull into, pull your vehicle off to the side of the road as far as possible. Once you come to a stop, turn off all lights except your hazard flashing lights, set the emergency brake, and take your foot off of the brake pedal to be sure the tail lights are not illuminated so that other drivers don't mistakenly run into you.