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Science with Steve: What the Fog?

A true sign of the autumn season is the roller coaster ride of a 7-day forecast, often times that comes with a few foggy mornings around the First Coast.

JACKSONVILLE, Fla. — Driving into work or school early on Wednesday morning and it looks like something straight out of a Stephen King novel. What the fog!?

A true sign of the autumn season around the First Coast are frequent changes in the weather day-to-day. After all, autumn is just a transition period between summer being hot and winter being cold, so really anything goes.

And within the weeks of ups and downs often comes the foggy morning.

Credit: wtlv weather
Fog rolling into downtown Jacksonville early Wednesday morning.

Fog is a cloud on the ground, simply put. The air overnight cools, reaching the dew point value and then becomes saturated. When the air is 100% saturated it condenses and voila, forms a cloud.

The dew point is a measure of moisture in the air, and for the meteorologists on the First Coast News Weather Team, it's the best way to tell whether it'll be a good or bad hair day. So the higher the dew point, higher the moisture content and higher the humidity.

Credit: wtlv weather
Temperatures vs. dew points Wednesday morning. The closer these two values are, the closer the air is to being 100% saturated.

On a moist day (like Tuesday was and parts of Wednesday will be), the dew point values hold in the 60s. Sure, it makes for a muggy day compared to the sweater weather this past weekend, but these dew points are what allows fog to form as easy as it did Wednesday morning.

When the sun sets, temperatures drop and the air cools down, trying to reach the dew point. So whenever the dew points are higher, they're more easily accessible. The temperature has no problem reaching the dew point, making it easier for a cloud to form right on the ground.