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FOG

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how and why dose it appear where it appears?

for instance driving to work today their where patches with no fog and places with quite dense fog.

yet on my way to tonight, their was a very small area of fog on around surrendered by no houses just fields.

sometimes it seems to form at the bottom of hills, yet on my way to work today was also fog up a hill.

it makes no sense and leaves my very puzzled :D

any help would be great

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two types of fog

radiation

advection, or often called sea fog

first one is due to radiative cooling of the bottom layers with clear skies and light winds with fairly long darkness hours which help

second one is warmer air advecting over a cold surface

sounds like it was the first one you experienced, fog forms in valley bottoms as cold air sinks down, especially likely near water, ponds, lakes, streams, rivers, to give the additional moisture.

Once the sun gets up then it starts to burn off the fog and can sometimes cause it to lift for a time into low cloud(Stratus). This is probably what you experienced at a higher location.

hope that helps

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yup dose a lot, one must stunning things we get on lewis sometimes is I live on point which is a separate island connected by one road. sometimes sea fog completely covers point whilst lewis itself is completely fog free looks amazing

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One of the things I often find striking, either at dusk or approaching dawn, is how, in still air, patches of gossamer like wafts of mist can occur, particularly over water or damp ground. In these conditions, even slight variations in surface are enough to increase water content, or reduce temperature (or both) such that mist forms here - and sometimes quite densely so too - but not there.

I still remember one Saturday evening in the winter of 1978/9 standing knee deep in the sno in the field next to my parents with most of my body below the inversion and my head and shoulders above it, with the differential around 2C from -11 to -13C. Very spooky.

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One of the things I often find striking, either at dusk or approaching dawn, is how, in still air, patches of gossamer like wafts of mist can occur, particularly over water or damp ground. In these conditions, even slight variations in surface are enough to increase water content, or reduce temperature (or both) such that mist forms here - and sometimes quite densely so too - but not there.

I still remember one Saturday evening in the winter of 1978/9 standing knee deep in the sno in the field next to my parents with most of my body below the inversion and my head and shoulders above it, with the differential around 2C from -11 to -13C. Very spooky.

Pity you didn't have a Photo of it.

Fog just seems a bit rare these days doesn't it.

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Fog just seems a bit rare these days doesn't it.

Not if you live here it doesn't, there's fog at some time or other on an average of 110 days a year although admittedly the majority of it is low cloud rather than radiation fog.

There are some spectacular sights at times though when the valleys are filled with fog up to 300mts or so and the hill tops are poking through it like islands.

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Fog just seems a bit rare these days doesn't it.

It seems to be getting less in the valleys I`m noticeing in recent years, all this week is given is mist or thicker mist at best mind that`s from the continental dry air I expect this week, although they are getting fog further east it seems now.

Mistiness by the streams also giving much more frost making it whiter.

As TM said though we still get plenty of hill fog and this winter`s been good for that but december was the best eg of freezing fog for 2 winters here coming from an east wind and there was fog even on low ground which doesn`t happen very often as have way down the hill it thinned out.

Had fog the other day also coming from the east as Teitis had sea fog earlier, it soon lifted into stratus next day though.

Last summer gave hill fog at times too even rarer to see hill fog in July quite thick. :huh:

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HI Cookie.

As others have said, fog, mist and clouds are all the same phenomena. That is, the air temperature has dropped such that it can no longer hold water in gasseous form.

This means two things are in play: temperature and pressure.

If temperature is held constant, the water vapour held in the air condenses out at as the air pressure reduces. This explains clouds and hill fog formation since air pressure drops with altitude. At altitude the air is forced to give up its water vapour because the pressure is not sufficient to support it.

Similarly, if pressure is held constant, water condenses out if the temperature drops (radiative).

Ground fog is therefore most common when static air pools and cools or when a cold mass of air meets warmer air with a high moisture content. (advection) The cooling forces the water vapour to condense. (Steam on a cold window effect).

At dusk on clear nights, the air cools and gets heavier. If the air is also still (as with static high pressure) it will sink and typically collects in valleys where it gets trapped. Its temperature continues to drop and its water vapour is forced to condense. Valleys also tend to be damp places because water runs off from the hills and also collects there. This is also true of streams and rivers or the sea or after a downpour of rain - anywhere the moisture content is higher.

In urban areas, the condensation is compounded by the presence of pollutants. Particulates in suspension (hygroscopic nuclei) the by-products of combustion - soot from fires, exhaust fumes, factory fumes etc, create dense and sometimes choking fogs as condensing water vapour forms much larger droplets around these particles. So called Smog, or smoke-fog.

London smogs in the late 1800's gave rise to the term 'pea-souper' to describe the density and colour of such fogs.

As others have noticed, with the general improvements in air cleanliness, thick fogs form less frequently because one of their anthropogenic mechanisms has been substantially reduced.

ffO.

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It seems to be getting less in the valleys I`m noticeing in recent years, all this week is given is mist or thicker mist at best.

Not today sunny here and quite low lying fog by the severn and as I went further north this afternoon it got more denser with some ice on the trees and grass in Oswestry, not sure what temps were but at a guess about 0.5 to 1c.

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