Why fog is thickest and most dangerous during the morning hours

Fog formation can happen quickly or take hours

Following fog, more sunshine in Central Florida ahead of cooler weather

ORLANDO, Fla. – Ever wonder why fog tends to thicken early in the morning, making the morning rush hazardous? There are a few factors.

Morning is the coolest time of the day. Sure, we call temperatures overnight lows, but it actually happens early in the morning. This time of day really sets the stage for fog development as temperatures drop to the dew point temperatures and the relative humidity approaches 100%.

Halloween morning will start off with areas of fog ranging from patchy to dense fog through midmorning. (WKMG)

Fog doesn’t just appear out of thin air. There are certain ingredients to make it happen.

In order for fog to appear, there has to be some sort of pollution or dust in the air for water vapor to condense around, and it has to be very humid outside. For example, sea fog forms around tiny particles of salt in the air. When the temperature and dew point of the air approach the same value or are less than 5 degrees Fahrenheit between each other, fog begins to show up. This can happen either by the air cooling like in advection, radiation or upslope fog, or by adding enough moisture to raise the dew point, like with steam or frontal fog.

Fog formation as the sun sets after the summer rain taken by meteorologist Samara Cokinos. (WKMG)

Radiation fog forms at night when the heat absorbed by the Earth’s surface during the day is radiated back into the air. Clear skies overhead allow this to happen the best, as there is no cloud cover to trap the heat trying to escape. The heat that’s transferred from the ground to the air forms tiny water droplets.

Advection fog forms when warm, moist air passes over a cool surface. When that moist, warm air makes contact with the cooler surface air, water vapor condenses to create fog. Advection fog shows up most frequently in places where warm, tropical air meets cooler ocean water.

Regardless of the type of fog, this type of weather on the morning commute can cause delays and hazards. Here are a few tips to stay safe.

Foggy roads expected for the Tuesday morning commute. Foggy conditions will gradually improve between 8a-10a. (Copyright 2022 by WKMG ClickOrlando - All rights reserved.)
  • Reduce your speed. Slowing down will give you enough time to react to something unseen in the distance, like a stopped car, pedestrian, or an animal that you see last minute due to reduced visibility.
  • Use roadside reflectors or the right edge of the road to help guide your drive. These markings can help alert and guide drivers safely around curves in the road that may not be visible due to dense fog. Using the right edge of the road helps by keeping commuters from drifting into other lanes.
  • Drive with low beams and fog lights. Using high beams/brights can actually reduce visibility even more when driving through fog. The brighter light reflects off the fog, unlike the low beams or fog lights that will help guide drivers through fog without the light reflecting back into the drivers’ eyes.
  • Increase your following distance from other cars. 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. This will help to ensure you have the proper time to respond to any obstacles hidden in the fog.
  • Minimize distractions. Put distractions like cell phones in a place where you won’t be tempted to reach for them while driving. Driving through fog requires both eyes on the road focusing on potential hazards that could be hidden in the fog and it keeps the driver from drifting off the road or into other lanes.
  • Watch out for animals and pedestrians. Fog acts like a camouflage giving bigger animals like deer, the confidence to move while under the cover of fog and not be seen by potential predators. This is a problem because drivers don’t see them and they don’t see the car until the last minute leaving little to no time to react. Pedestrians may be walking alongside the road in fog too and that includes children or teens headed to the bus stop. If the pedestrians are wearing a brighter color it will help to reflect the light from the car, but darker colors will be more difficult to see. Also, keep in mind smaller children may not pay attention or see a car before darting across the road to get to the bus stop.

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About the Author:

Emmy Award Winning Meteorologist Samara Cokinos joined the News 6 team in September 2017. In her free time, she loves running and being outside.