Hill Fog - how ?

Went out for a bite to eat last night. Misty when we went , but coming home the fog on the top of Parbold hill was down to about 30 yards visibility. Now they did mention hill fog on the weather today. But if fog/mist is heavy , you can see it in valley bottoms , why does it stick on top of a hill When we drove down to the bottom it was just a light mist.

 

There was one sat on the A35 yesterday. It's there so often there's warning signs up

 

Think is something to do with hot and cold air, we don't get hill fog here but we do get sea fog and rolling mist as we are at sea level

Copyed from the net

Evaporation fog is caused by cold air passing over warmer water or moist land. It often causes freezing fog, or sometimes Types of frost. When some of the relatively warm water evaporates into low air layers, it warms the air causing it to rise and mix with the cooler air that has passed over the surface.

 

I tend to think hill fog is actually low cloud.
Whereas fog that forms in hollows forms by a different means, ie. cold air dropping down hillsides and creating a cold pool of air,(similar to frost hollows), which cannot then hold the same amount of moisture as the slightly warmer air higher up, so the water condenses and forms fog.
Often river valleys contain fog on cold mornings due to the cold air collecting and the damper atmosphere.

Of course I could be talking rubbish.

 

Don't think you're talking rubbish at all, @pete. There are lots of hills and valleys round here and when you're driving around, you can see the low cloud from a distance, sat on a hilltop like a big fluffy cushion. Then there's the normal fog, especially in the river valleys. And the French reckon that it's always foggy or raining in the UK! Errr...

 

Fog and cloud are basically the same things. Its just that we as humans are used to calling low clouds fog...

As regards hill fog. Simply put, its moist air that drifts uphill, and cools as it does so. At the bottom of the hill it would have been damp (high humidity) conditions.

 

Well, no....clouds are (usually) in the sky? When weather conditions dictate that the cloud cover is dense and relatively low, it stands to reason that the high ground of hilltops meets the low cloud. Dammit, I'll have to get some photos to confirm the thesis

 

Thesis bigger than both of us

There was a cloud that parked on a hill for 3 days and emitted sparks and hooting noises

 

Was it training, waiting for its opportunity to make its name?

 

What are you lot on?? And could you send me some, please?

 

I get a lot here in Wales and I call it low cloud on top of the hills

 

Well, er...yes....Clouds, fog, mist are all different terms for visible water vapour. What this is called depends on where it is. Up in the sky, we call it clouds. Down on the ground, fog or mist. Somewhere in between, hill fog or low cloud, dependent on the height of hill or mountain.

One term for visible water vapour that really gets me is when the white stuff coming out of a boiling kettle is called "steam." Its not. If it was, we could not see it...

@Zigs wasnt the cloud parked on the hill for three days emitting sparks and hooting noises the one in Cornwall? The one they moved to Washington?

 

So it seems that "hill fog" is the low level cloud Stratos . Lovely name but 'orrible stuff ! It covers everything and often is full of light drizzle.
Yet another problem solved by GC

Stratus clouds