Dense fog advisory issued for South Florida, why fog forms

The National Weather Service issued a dense fog advisory this morning warning of fog with visibility levels down to one-quarter mile in some locations.

The advisory is in effect until 10 a.m.

It’s been a familiar refrain the past two weeks, with drivers being urged to use low beams and leave plenty of space between vehicles.

Dense fog advisory in effect until 10 a.m.

But why so foggy?

In South Florida, fog is usually an early morning hazard that can happen on clear nights with light winds.

Florida fog often forms when warm, moist air off the water comes into contact with the nighttime cooling surface of the Earth.

The temperature lowers to the dew point temperature, becomes fully saturated with water vapor, and fog occurs. The dew point is the temperature at which the air becomes 100 percent saturated.

Fog is basically a surface-level stratus cloud.

Check The Palm Beach Post radar map.

Measurements from PBIA this morning show the temperature dropping to the dew point temperature before dawn.

Among Florida cities, Tallahassee has the highest frequency of fog, while Key West has virtually no incidents of fog, according to the book “Florida Weather” by Morton D. Winsburg.

The National Weather Service sends out a special weather statement when visibility is reduced to one-half mile. If visibility dips to one-fourth mile, a fog advisory is issued.

Dense fog is rare in Florida. Between 2000 and 2011, NOAA’s storm events database recorded just 35 days during which dense fog was present statewide. But those incidences can be lethal.

The database lists five deaths and 17 injuries directly attributable to dense fog, while Palm Beach Post archives list multiple car accidents in which fog was involved.

Download the Palm Beach Post WeatherPlus app here.

In March 2007, Boynton Beach resident Anita Zoet died after her car plowed into an 18-wheeler on Florida’s Turnpike in heavy fog. Four others were also killed in the accident that included a 12-vehicle pileup.

A year earlier, two people were killed and 20 injured in western Palm Beach County when smoke combined with fog to reduce visibility on State Road 80 and U.S. 27.

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What is fog and why does it happen in South Florida?

In South Florida, fog is usually an early morning hazard that can happen on clear nights with light winds.

Among Florida cities, Tallahassee has the highest frequency of fog, while Key West has virtually no incidents of fog, according to the book “Florida Weather” by Morton D. Winsburg.

Florida fog often forms when warm, moist air off the water comes into contact with the nighttime cooling surface of the Earth. The temperature lowers to the dew point temperature, becomes fully saturated with water vapor, and fog occurs. The dew point is the temperature at which the air becomes 100 percent saturated.

Fog is basically a surface-level stratus cloud.

Check The Palm Beach Post radar map.

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The National Weather Service sends out a special weather statement when visibility is reduced to one-half mile. If visibility dips to one-fourth mile, a fog advisory is issued.

Dense fog is rare in Florida. Between 2000 and 2011, NOAA’s storm events database recorded just 35 days during which dense fog was present statewide. But those incidences can be lethal.

The database lists five deaths and 17 injuries directly attributable to dense fog, while Palm Beach Post archives list multiple car accidents in which fog was involved.

Download the Palm Beach Post WeatherPlus app here.

Dense fog this morning obscures islands in the Intracoastal between West Palm Beach and Palm Beach.  Photo by Eddie Ritz
Dense fog this morning obscures islands in the Intracoastal between West Palm Beach and Palm Beach. Photo by Eddie Ritz

In March 2007, Boynton Beach resident Anita Zoet died after her car plowed into an 18-wheeler on Florida’s Turnpike in heavy fog. Four others were also killed in the accident that included a 12-vehicle pileup.

A year earlier, two people were killed and 20 injured in western Palm Beach County when smoke combined with fog to reduce visibility on State Road 80 and U.S. 27.

If you haven’t yet, join Kim on Facebook, Instagram and Twitter.

Foggy morning, afternoon storms expected in Palm Beach County

National Weather Service forecasters are expecting another foggy morning in Palm Beach County on Wednesday as light winds, moist air and temperatures come together.

Check The Palm Beach Post radar map.

Forecasters issued a special weather advisory Tuesday morning warning of dense, patchy fog throughout South Florida and visibility reduced to one mile or less.

In a hazardous weather outlook issued Tuesday afternoon, meteorologists said conditions are good again for fog to form late Tuesday night and early Wednesday morning. In the thickest fog, visibility could be reduced to less than a quarter mile.

 

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Download the Palm Beach Post WeatherPlus app here.

Fog, which is basically a surface-level  stratus cloud, occurs when the temperature lowers to the dew point and winds are low. Also, southwest winds will be blowing in moisture, keeping the dew point high.

There is still a chance for afternoon thunderstorms Wednesday as a cold front pushes through. The Storm Prediction Center has Central Florida under a marginal risk for severe weather Wednesday.

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Why it’s been so foggy in South Florida this week, alert issued this morning

The National Weather Service issued a special weather statement this morning warning of widespread patchy fog throughout South Florida, including western and coastal Palm Beach County.

Some isolated areas are experiencing dense fog where visibility is down to around a half mile, or even less.

“Motorists should exercise caution this morning across all of South Florida,” the statement says. “A gradual clearing through is expected through mid morning.”

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Fog can be caused when the temperature lowers to the dew point temperature and when winds are low.

Observations taken at Palm Beach International Airport this morning, show the temperature plunging in the early morning hours to nearly equal the dew point temperature of about 63 degrees. Dew point measures the amount of water vapor in the air. When the dew point temperature and air temperature meet, there is 100 percent saturation.

At the same time winds this morning are blowing very lightly out of the northwest, allowing the moisture to settle.

The combination contributed to the fog, which is a surface-level stratus cloud. (Note in the second box the cloud level significantly drops during when the fog is present.)

Fog is simply a low cloud in contact with the surface.

The temperature (purple line) and dew point temperature (green line) nearly met early this morning, helping create fog.
The temperature (purple line) and dew point temperature (green line) nearly met early this morning, helping create fog.

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Dense fog is rare in Florida. Between 2000 and 2011, NOAA’s storm events database recorded just 35 days during which dense fog was present statewide. But those incidences can be lethal.

The database lists five deaths and 17 injuries directly attributable to dense fog, while Palm Beach Post archives list multiple car accidents in which fog was involved.

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Successful launch of CYGNSS mission

Patchy dense fog a concern for drivers this morning

The National Weather Service has issued a special weather statement warning of patchy dense fog across portions of inland Palm Beach Palm Beach County.

The main concern is along portions of Alligator Alley and areas around Lake Okeechobee.

In worse case scenarios, visibility could be reduced to less than half a mile.

The fog is expected to burn off quickly once the sun rises. The statement is in effect until 8 a.m.

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