fog

Who Knew There Were So Many Kinds Of Fog?

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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.

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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].

Monday weather: Morning fog, then sun and highs around 47

Forecasters expect mostly sunny skies throughout the mid-valley on Monday, at least after patches of morning freezing fog burn off. Highs Monday will be around 47. Freezing fog is expected Monday night, as temperatures dip to the lower 20s. More sunshine and highs around 51 are expected on Tuesday.

Weekend weather: Sunny Saturday, but showers Sunday

It’s a split decision for the weekend, forecasters say: Saturday should be mostly sunny throughout the mid-valley, with highs around 52. But clouds will begin rolling in on Saturday night, with temperatures falling to around 32, and showers are likely on Sunday, along with highs near 47.

Thursday weather: Patches of morning fog, then mostly cloudy

Expect patches of morning fog throughout the mid-valley on Thursday, forecasters say, and mostly cloudy skies after that. Highs Thursday will be around 57. Mostly cloudy tonight, with lows around 40. Partly sunny on Friday, with highs in the lower 50s. 

Tuesday weather: Morning fog, then partly sunny skies

After the morning fog clears off, forecasters expect partly sunny skies throughout the mid-valley on Tuesday, with highs in the mid-50s. Patches of fog should reappear Tuesday night, with lows dipping into the mid-30s.

Monday weather: Patchy morning fog, then sunny

Here’s a pattern to get used to for this week’s weather: Forecasters say to expect patchy fog in the morning, but when that clears, we’ll be seeing sunny skies. Monday’s forecast follows that formula; Patchy fog, then sun, with highs in the mid-50s. Monday night will be mostly cloudy, with lows around 40.

What’s The Difference? It Can Be Important.

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In today’s world there are people pointing out differences sometimes for good purposes and sometimes not so good. Color differences, political differences, religious differences, geographical differences and the list goes on. That’s also the case with the weather, particularly this time of the year when some differences can lead to confusion and even accidents.

Dense Fog
Dense Fog Seen From Peace Health Riverbend Hospital | Image Tim Chuey

We have had and will continue to have advisories for fog, dense fog, freezing fog, and frost throughout the winter months.The subsidence caused by high pressure closes off the mixing of the air at the surface which means anything that is at or near the surface stays there. Some of those things include smoke, which I discussed in my last column article, fog, freezing fog, and frost. The differences can be subtle, but they can also be dangerous.

Let’s start with fog. I remember in school the first definition I was taught. We were told that fog is a cloud that is close to or touches the ground. The National Weather Service officially defines fog this way: “Fog is water droplets suspended in the air at the earth’s surface. Fog is often hazardous when the visibility is reduced to 1/4 mile or less.”

Radiation Fog
Radiation Fog | Image by slideplayer.com

Fog is just fog, right? No. Actually there are eight major kinds of fog. Let’s take a look at them to see how they differ. The following descriptions are from weather.com.

1) Radiation fog: This forms when all solar energy exits the earth and allows the temperature to meet up with the dew point. The best condition to have radiation fog is when it had rained the previous night. This helps to moisten up the soil and create higher dew points. This makes it easier for the air to become saturated and form fog. However, the winds must be light, less than 15 miles per hour, to prevent moist and dry mixing.

2) Precipitation fog: This is fog that forms when rain is falling through cold air. This is common with warm fronts but it can occur with cold fronts as well only if it is not moving too fast. Cold air, dry at the surface, while rain is falling through it evaporates and causes the dew point to rise. This saturation forms fog.

Advection Fog
Advection Fog | Image by weather.gov

3) Advection fog: This type of fog forms from surface contact with horizontal winds. This fog can occur with windy conditions. Warm air, moist air blows in from the south and if there is snow or cool moisture on the ground will come in contact with the warm, moist winds. This contact between the air and ground will cause the air blowing in to become cool. Then dew point rises and creates high humidity and forms fog.

4) Steam fog: This type of fog is commonly seen in the Great Lakes but can be seen on any lake. This forms in the fall season. As summer ends, water temperatures don’t cool right away but air temperature does. As a mass of dry cool air moves over a warmer lake the the warm lake conducts warm, moist air into the the air mass above. This transport between the lake and air evens out. This corresponds to the second law of thermodynamics and this law states  “any two bodies that come into contact, the system will become equilibrium state.” Steam fog does not become very deep but enough to block some of the sunlight.

5) Upslope fog: This fog forms adiabatically. Adiabatically is the process that causes sinking air to warm and rising air to cool. The cooling of the air from rising causes it to meet up with the dew point temperature. Fog forms on top of the mountains.

6) Valley fog: This fog forms in the valley when the soil is moist from previous rainfall. As the skies clear solar energy exits earth and allows the temperature to cool near or at the dew point. This forms deep fogs so dense it’s sometimes called tule fog.

Fog
Fog With Freezing Fog On The Grass| Photo by Tim Chuey

7) Freezing fog: Freezing fog occurs when the temperature falls to 32 degrees F (0 degrees C) or below. This fog produces drizzle, and these tiny droplets freeze when they come into contact with an object. But at the same time sublimation is going on.

8) Ice fog: This type fog is only seen in the polar and arctic regions. Temperatures at 14 degrees F (-10 degrees C) are too cold for the air to contain super-cooled water droplets it forms small tiny ice crystals.

Now we’ll discuss frost. According to nationalgeographic.com “Frost is water vapor, or water in gas form, that becomes solid.” “Frost forms when an outside surface cools past the dew point. The dew point is the point where the air gets so cold, the water vapor in the atmosphere turns into liquid. This liquid freezes. If it gets cold enough, little bits of ice, or frost, form. The ice is arranged in the form of ice crystals.”

There are four main types of frost. Here’s how The National Geographic Society describes them.

Hoarfrost
Radiation Frosty (Hoarfrost) | Photo by pixabay.com

1) Radiation frost ( also known as hoarfrost) is frost in the form of tiny ice crystals that usually shows up on the ground or exposed objects outside. Hoarfrost also forms in refrigerators and freezers.

Advection Frost
Advection Frost | Photo by nationalgeographic.org

2) Advection frost is a collection of small ice spikes. Advection frost forms when a cold wind blows over the branches of trees, poles, and other surfaces.

3) Window frost forms when a glass window is exposed to cold air outside and moist air inside. Window frost is familiar to winter residents of cold climates. Indoor heat and cold outdoor temperatures form this type of frost. Window frost was much more common before people began using double-paned windows.

4) Rime frost is frost that forms quickly, usually in very cold, wet climates. Rime also forms in windy weather. Rime sometimes looks like solid ice. Ships traveling through cold places like the Arctic Ocean often end up with rime covering at least part of the exposed part of the ship.

We have been experiencing a combination of fogs and frost. Our fog combination is radiation fog and freezing fog with some mainly radiation frost. The one good thing about having dense fog when freezing fog and frost are present (if there can be anything good about the situation) is that the fog can lower visibility enough that drivers must slow down to see where they are going. If they are moving at a slower speed when they encounter slippery spots on the roadway there is a better chance they will be able to keep the car under control and not experience an accident

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

It Comes On Little Cat Feet.

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Carl Sandburg wrote about it. London is famous for it. Airline flights have been delayed and even cancelled because of it and if the surface temperature is at or below freezing it can cause very slippery road conditions. It should be obvious that I am talking about fog.

Carl Sandburg's Fog.jpg | image by www.youtube.com
Carl Sandburg’s Fog.jpg | image by www.youtube.com

Here is the short and sweet of Carl Sandburg’s famous poem. ” The fog comes on little cat feet. It sits looking over the harbor and city on silent haunches and then moves on.”

You might remember being taught 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 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.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
Yaquina Head Lighthouse In Fog | Photo By Tim Chuey

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 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, something we have been familiar with lately, 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.

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