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uk.sci.weather (UK Weather) (uk.sci.weather) For the discussion of daily weather events, chiefly affecting the UK and adjacent parts of Europe, both past and predicted. The discussion is open to all, but contributions on a practical scientific level are encouraged. |
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#1
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I was out in the countryside from dawn this morning. As we under a big high pressure area, there was mist in the valleys that had formed overnight as air in contact with a cooling surface flowed downhill and it's water vapour turned to droplets. All straight out of a text book. What I do not understand is why cloud formed as the sun came up and soon blocked out the sun.
So my question - how does cloud (not ground level mist) form in sinking air? |
#2
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Steve Wood wrote:
I was out in the countryside from dawn this morning. As we under a big high pressure area, there was mist in the valleys that had formed overnight as air in contact with a cooling surface flowed downhill and it's water vapour turned to droplets. All straight out of a text book. What I do not understand is why cloud formed as the sun came up and soon blocked out the sun. So my question - how does cloud (not ground level mist) form in sinking air? Low-level turbulent mixing caused by convection underneath the subsidence inversion is likely to be the main cause. When the cloud tops reach the inversion they spread out resulting in a layer of stratocumulus. -- Norman Lynagh Tideswell, Derbyshire 303m a.s.l. |
#3
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![]() Low-level turbulent mixing caused by convection underneath the subsidence inversion is likely to be the main cause. When the cloud tops reach the inversion they spread out resulting in a layer of stratocumulus. Mostly found over Weston Coyney and Tideswell ![]() Graham |
#4
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![]() Low-level turbulent mixing caused by convection underneath the subsidence inversion is likely to be the main cause. When the cloud tops reach the inversion they spread out resulting in a layer of stratocumulus. Mostly found over Weston Coyney and Tideswell ![]() Graham |
#5
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![]() Low-level turbulent mixing caused by convection underneath the subsidence inversion is likely to be the main cause. When the cloud tops reach the inversion they spread out resulting in a layer of stratocumulus. Mostly found over Weston Coyney and Tideswell ![]() Graham |
#6
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On 23/09/2013 22:10, Graham wrote:
Low-level turbulent mixing caused by convection underneath the subsidence inversion is likely to be the main cause. When the cloud tops reach the inversion they spread out resulting in a layer of stratocumulus. Mostly found over Weston Coyney and Tideswell ![]() Graham And also Wolverhampton ! ;-) |
#7
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On Monday, 23 September 2013 17:07:22 UTC+1, Steve Wood wrote:
I was out in the countryside from dawn this morning. As we under a big high pressure area, there was mist in the valleys that had formed overnight as air in contact with a cooling surface flowed downhill and it's water vapour turned to droplets. All straight out of a text book. What I do not understand is why cloud formed as the sun came up and soon blocked out the sun. So my question - how does cloud (not ground level mist) form in sinking air? -- Steve Wood The air in which the cloud is formed is not sinking. The base of the subsidence inversion rarely descends to below about 3000 ft. If it had been in midsummer the cooler air beneath the inversion could have been warmed out enough for the inversion to disappear. There would still have been convective cloud, maybe quite large, but it would have spread out in the way it has done in the last few days. Another factor about the current situation is that the lower layers are rather moist, more so than usual. Tudor Hughes, Warlingham, Surrey. |
#8
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On 23/09/2013 22:40, Joe Egginton wrote:
On 23/09/2013 22:10, Graham wrote: Low-level turbulent mixing caused by convection underneath the subsidence inversion is likely to be the main cause. When the cloud tops reach the inversion they spread out resulting in a layer of stratocumulus. Mostly found over Weston Coyney and Tideswell ![]() Graham And also Wolverhampton ! ;-) And Cheltenham... -- Paul Hyett, Cheltenham |
#9
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![]() Quote:
Thanks for your replies - this does make sense and agrees with what I observed. (Though it is still annoying when I want to take a photograph of valley mist lit by the sun!). |
#10
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In article ,
Tudor Hughes writes: On Monday, 23 September 2013 17:07:22 UTC+1, Steve Wood wrote: I was out in the countryside from dawn this morning. As we under a big high pressure area, there was mist in the valleys that had formed overnight as air in contact with a cooling surface flowed downhill and it's water vapour turned to droplets. All straight out of a text book. What I do not understand is why cloud formed as the sun came up and soon blocked out the sun. So my question - how does cloud (not ground level mist) form in sinking air? -- Steve Wood The air in which the cloud is formed is not sinking. The base of the subsidence inversion rarely descends to below about 3000 ft. If it had been in midsummer the cooler air beneath the inversion could have been warmed out enough for the inversion to disappear. There would still have been convective cloud, maybe quite large, but it would have spread out in the way it has done in the last few days. Should that read "not have spread out"? Another factor about the current situation is that the lower layers are rather moist, more so than usual. Tudor Hughes, Warlingham, Surrey. I think this must be a tricky time of year for forecasters with this set-up. A month ago they could have been confident that the cloud would have been "burnt off", and in a couple of months time they could have been confident that it wouldn't have been, but in late September and through October it tends to be touch and go. -- John Hall "Distrust any enterprise that requires new clothes." Henry David Thoreau (1817-1862) |
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