Coastal fog forms, may be a more widespread issue tonight

Mark Collins delves into fog forecasting

By Rebecca Barry - Meteorologist, Mark Collins - Meteorologist

JACKSONVILLE, Fla. -  

Coastal fog is rolling in along the Beaches once again today, and it may be a more widespread issue overnight. 

Meteorologist Mark Collins explains different ways to detect fog, "Its best to look at GOES 16 satellite data to see where the fog is located.  This will show the fog banks offshore. Winds determine if it will roll in or not, but too much of it can also dissipate fog deck. Light east winds under 5 mph are best for pushing fog in to the coast." 

Mark's Favorite Links for Fog

Click here for the College of Dupage's visible satellite loop. But often, fog can be hidden by upper level clouds flowing northeast from the Gulf over Jacksonville.

So I often look here, this shows thick sea fog in white off the Georgia and South Carolina coast. 

Over land fog symbols on weather charts are indicated by 2 horizontal short lines on stacked together. This page would highlight areas below 1 mile visibility.

This link is for nighttime only views of clouds and is useful for discriminating between different cloud types like low stratus clouds and fog. Fog will show up as white in the color enhancement. Stratus will also appear white but often has greater movement to the clouds viewing the animation. 

Finally, this model is useful for predicting fog. The magenta​ colors are cloud ceilings less than 500 feet and/or visibility is less than 1 mile. Even experienced IFR pilots may have a hard time flying in these foggy conditions.

​Even with all this information the ephemeral nature of fog makes it very difficult to time out.  

How Fog Forms

Fog forms when the temperature drops within a couple of degrees of the dewpoint, all of the moisture in the air condenses out, in the form of a cloud, at the ground level.  Quiet weather patterns, with consistent broad swings in temperature make for fog prone mornings. The warm afternoon temperatures  allow for more absorption of moisture in the atmosphere, making you more likely to see fog when the temperatures cool down and the atmosphere can't hold as much moisture.

Fog dissipates when temperatures warm up. As the temperatures warm, the atmosphere can once again hold a higher capacity of moisture, so the droplets of water that make up the cloud are absorbed into the air.

Many times, fog will be more persistent and linger over large bodies of water, like the ocean or the river. The temperature changes diurnally more rapidly over land than the water, so as the land warm up more quickly, the fog dissipates first over the land.

The National Weather Service issues Dense Fog Advisories when they anticipate the potential for widespread visibilities reduced to less than a quarter of a mile. When visibility on the road is less than a quarter of a mile, that is the threshold for what is considered hazardous to drive in. 

Driving in fog can feel like driving while wearing a blindfold. Objects, such as other vehicles or traffic signals, may not be visible until the last moment- sometimes too late to take proper corrective action.

The two most important safety measures when you driving in fog are to slow down and turn on your low-beam headlights. By reducing speed, you increase available reaction time. And driving with your low-beam headlights on helps you to see the roadway more clearly and increases your visibility.

Additional tips for driving in fog
Use your windshield wipers to increase your visibility and reduce glare from oncoming vehicles.

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If your vehicle is equipped with daytime running lights (DRLs), you may need to manually turn on your headlights, so your tail lights will also be illuminated.
Avoid sudden stops – and remember that larger vehicles need more distance to slow down or stop.

If you must stop, steer off the roadway as far as safely possible.

The use of hazard lights in inclement weather is illegal in Florida. However, it is permitted in Georgia.

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