freezing fog

Who Knew There Were So Many Kinds Of Fog?

/////

Lately it has been difficult to see the morning sky and that is the result of fog, often quite dense. The Autumn season is when fog seems to begin to develop more often and continues through Winter.  We were all taught way back in our general science class that fog is just a cloud that touches the ground. That is a gross understatement of the facts which are not quite that simple. It takes specific conditions of temperature and humidity to produce fog and there are actually many kinds of fog determined by exactly how it is formed.

Dense Fog
Dense Fog In South Eugene | Photo by Tim Chuey

One thing you have to understand before we proceed is what it takes to make fog. To do that we need to define a meteorological term that is used in the creation of fog. That is the dewpoint temperature. The dewpoint temperature is the temperature to which air must be cooled at constant pressure for saturation to occur, followed by condensation.

Dewpoint
Dewpoint/Relative Humidity | Image by sldph.com

The relationship between the dewpoint temperature and the ambient air temperature is shown by the relative humidity expressed as a percentage. The closer the dewpoint temperature is to the ambient air temperature the higher the relative humidity and when they are the same number the relative humidity is 100%. Some of the varied types of fog are advection fog, radiation fog or ground fog, upslope fog or hill fog, steam fog or evaporation fog or sea smoke, precipitation fog, freezing fog, valley fog, and fog stratus. I’m sorry if I am taking away some of the mystique of fog but now is the time to explain the various kinds I have listed for you. Some of the difference are subtle, but I think it’s interesting to see how much something we take so much for granted has been studied and explained.

Well start with advection fog. It forms when moist air pushed by the wind passes over a cool surface and is cooled. Advection fog is most commonly found over the ocean as the moist air sweeps over the cooler water. Radiation fog, also called ground fog, is formed by the cooling of the ground after sunset by thermal radiation that rises when the wind is calm with clear skies.

Upslope Fof
Upslope Fog | Image by learningtoflyblog.com

Upslope fog or hill fog is produced when winds blow air up a slope cooling it as it rises and causing the moisture to condense out. This can also cause freezing fog on mountain tops. Steam fog, evaporation fog, or sea smoke is created by cold air passing over warmer water or moist land. It often causes freezing fog or sometimes even hoar frost. Precipitation fog, also called frontal fog, forms as precipitation falls into drier air below the cloud and the liquid droplets evaporate into water vapor. The resultant water vapor cools forming fog. Freezing fog is fog that  has its droplets of moisture freeze to a surface the temperature of which is at or below freezing. Valley fog forms in mountain valleys often in winter. It is a radiation fog that is trapped in a relatively narrow space.

Fog Stratus
Fog Stratus | Photo by sites.google.com

The last type of fog I have listed is fog stratus which is a layer of fog that acts like a cloud in that it can stay higher above the ground surface and then lower to the ground often causing very dense fog and even freezing fog if the surface (particularly streets, driveways and sidewalks) or objects like roofs are cooled to levels at or below freezing. There may be a few other kinds of fog, but they would be combinations of what I have already described or so close in definition that it wouldn’t be significant. I don’t know about you, but I still am in awe  of one of natures coolest creations, fog.

Fog Headlights
Headlights In Fog | Photo by youtube.com

There is one big favor you can do for me and all of the other  people driving in foggy weather and that is USE YOUR LOW BEAM HEADLIGHTS NOT HIGH BEAM. The high beam shows you more fog and is more difficult to see through while blinding oncoming drivers with a bright wall of fog which means they can’t see where you are.

Let me know what you would like me to talk about or explain. You can comment below or email me at: [email protected].

Using Your High Beams Makes It Worse.

/////

This time of the year we have many weather elements that can and do make driving on our roadways hazardous. We have snow, blowing snow, freezing rain, hail, frost, ice, and fog. How many times have you been driving along without a care in the world when you come upon an area of fog?

Fog Headlights
Headlights In Fog | Photo by youtube.com

You turn your headlights on so you can see better and so your vehicle can be seen by oncoming traffic. Then suddenly you are blinded by the fog because the car coming at you has their high beams on. That is the first rule of driving in foggy conditions. Turn on your headlights, but low beam only. The high beam lights only light up the fog making it more difficult for you to see and for you to be seen.

Dense Fog At PeaceHealth Sacred Heart Hospital River Bend | Photo By Tim Chuey

You might remember being taught in school way back in your general science class that fog is just a cloud that touches the ground. That is a gross understatement of the facts which are not quite that simple. It takes specific conditions of temperature and humidity to produce fog and there are actually many kinds of fog determined by exactly how it is formed. One thing you have to understand before we proceed is what it takes to make fog. To do that we need to define a meteorological term that is used in the description of the creation of fog. That is the dewpoint temperature. (That means the air is holding as much moisture as it can.) The dewpoint temperature is the temperature to which air must be cooled at constant pressure for saturation to occur, followed by condensation.The relationship between the dewpoint temperature and the ambient air temperature is shown by the relative humidity expressed as a percentage. The closer the dewpoint temperature is to the ambient air temperature the higher the relative humidity and when they are the same number the relative humidity is 100%. Some of the varied types of fog are advection fog, radiation fog or ground fog, upslope fog or hill fog, steam fog or evaporation fog or sea smoke, precipitation fog, freezing fog, valley fog, and fog stratus. I’m sorry if I am taking away some of the mystique of fog but now is the time to explain the various kinds I have listed for you. Some of the difference are subtle, but I think it’s interesting to see how much something we take so much for granted has been studied and explained.

Yaquina Head Lighthouse In Fog | Photo By Tim Chuey

First we start with advection fog. It forms when moist air pushed by the wind passes over a cool surface and is cooled. Advection fog is most commonly found over the ocean as the moist air sweeps over the cooler water. Radiation fog, also called ground fog, is formed by the cooling of the ground after sunset by thermal radiation that rises when the wind is calm with clear skies. Upslope fog or hill fog is produced when winds blow air up a slope cooling it as it rises and causing the moisture to condense out. This can also cause freezing fog on mountain tops. Steam fog, evaporation fog, or sea smoke is created by cold air passing over warmer water or moist land. It often causes freezing fog or sometimes even hoar frost. Precipitation fog, also called frontal fog, forms as precipitation falls into drier air below the cloud and the liquid droplets evaporate into water vapor. The resultant water vapor cools forming fog.

Fog/ Freezing Fog
Frost/Freezing Fog 3 | Photo by Tim Chuey

Freezing fog, something we have been familiar particularly during the winter months, is fog that  has its droplets of moisture freeze to a surface the temperature of which is at or below freezing. Valley fog forms in mountain valleys often in winter. It is a radiation fog that is trapped in a relatively narrow space.

Fog
Dense Fog Stratus In South Hills | Photo By Tim Chuey

The last type of fog I have listed is fog stratus which is a layer of fog that acts like a cloud in that it can stay higher above the ground surface and then lower to the ground often causing very dense fog and even freezing fog if the surface (particularly streets, driveways and sidewalks) or objects like roofs are cooled to levels at or below freezing. There may be a few other kinds of fog, but they would be combinations of what I have already described or so close in definition that it wouldn’t be significant. I don’t know about you, but I still am in awe of one of natures coolest creations, fog.

Let me know what you would like me to talk about or explain. You can comment below or email me at: [email protected].

February 28 – Morning Headlines

//

Headlines

City extends the exclusion zone till November. Is that long enough, or has it been too long already?
  • Driver arrested in fatal accident
    Police arrested a 53-year-old Springfield man Sunday in connection with an August traffic accident that killed a female bicyclist on River Road. James Robert Gleich was booked into the Lane County Jail on charges of first-degree manslaughter, criminall…
  • Fire Heavily Damages Eugene Duplex
    Fire investigators are still trying to figure out how a Eugene duplex went up into flames early Monday morning. It happened in an apartment complex on North Polk Street just after 6 a.m. Firefighters say the fire broke out on an upstairs floor. T…
  • AAA: OR gas price $3.89, up 23 cents in a week
    The AAA auto club reports the average price of gasoline in Oregon is $3.89 a gallon.
  • Council extends downtown exclusion zone — through November
    Eugene’s downtown exclusion zone will live awhile longer, but not nearly as long as supporters had hoped. The City Council late tonight voted to extend the controversial ordinance until Nov. 30. Supporters had wanted the ordinance to last for another…
  • Rideshare resources to save on gas
    As gas prices rise, Lane Transit District wants residents to log onto their new resource Drive Less Connect. It’s a rideshare database where users can find other commuters going their…

Tim Chuey Weather:

Your Tuesday will start off with possible fog and freezing fog, then increasing clouds with the chance of rain increasing, and maybe even some snow by nightfall.

High: 46
Low: 35
Rain: up to 1inch.

Forecast for the Southern and lower Mid Willamette Valley including Eugene-Springfield and Albany-Corvallis: Partly cloudy with patchy fog and freezing fog this AM, increasing clouds to mostly cloudy with rain becoming likely (60%) this afternoon (0.25 in. of rain possible), rain in the evening, rain and snow showers (snow level 500 ft. to 1,000 ft. late at night, 1 in. of snow possible, 0.50 in. of rain possible) late tonight and windy (S 15-25 mph), mostly cloudy with rain and snow showers Wednesday (small hail possible), rain and snow showers Wednesday night, rain and snow showers likely (60%) Thursday, then a (40%) chance of showers Thursday night highs 43-46 lows near 35. Mostly cloudy with a (40%) chance of rain Friday and Friday night, a  mix of clouds and sun with a good (50%) chance of rain Saturday, a (30%) chance of showers Saturday night, a slight (20%) chance of showers Sunday, cloudy with a (40%) chance of rain Sunday night, then a good (50%) chance of rain Monday highs 45-54 cooling to near 50 Monday lows 35-40 cooling to 36 Sunday night. (seasonal averages high 53 low 36)

Because weather forecasting is a combination of science, intuition, and timing there can be no absolute guarantees that individual forecasts will be 100% accurate. Nature is in a constant state of flux and sudden unexpected weather events can happen.

Keep Current on the Weather: timchueyweather4u.com