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Hi I had a question about Freezing fog that I don't seem to be able to find the awnsers for by google searching. Its my favourite type of weather phenomenon but I don't get to see it very often in my part of the world (Thames Valley/Marlborough Downs)

We get plenty of fog here, autumn and winter, and there are many frost pockets and hollows but getting frost and fog at the same time always seems to be rare. I know freezing fog is brought about obviously by sub zero temperatures and areas of clear high pressure in winter, by why is that some clear some frosty highs produce freezing fog occaisonally while many more usually don't? 
What are the exact conditions needed for it to form other than clear highs and very low temps? 

During December 2010 we had almost 3 weeks of lying snow under both cloudy and clear conditions and freezing fog formed on only one of those nights. It was neither the mildest or the coldest night either.  I see a lot of people mention on forums when looking at certain charts that due to what they see, freezing fog could definitely be a risk. What is it about a particular chart that makes a cold frosty high more likely to produce FF than another?  It would be a great help if anyone could explain the partiuclar conditions that create the right sort of environment for FF to occur locally. Does it have to do with relative humidity? direction of source of cold air? How moist the ground is? 

Thank you for any helpful explanation.

freezing fog.jpg

Edited by Atleastitwillbemild
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4 hours ago, Atleastitwillbemild said:

Hi I had a question about Freezing fog that I don't seem to be able to find the awnsers for by google searching. Its my favourite type of weather phenomenon but I don't get to see it very often in my part of the world (Thames Valley/Marlborough Downs)

We get plenty of fog here, autumn and winter, and there are many frost pockets and hollows but getting frost and fog at the same time always seems to be rare. I know freezing fog is brought about obviously by sub zero temperatures and areas of clear high pressure in winter, by why is that some clear some frosty highs produce freezing fog occaisonally while many more usually don't? 
What are the exact conditions needed for it to form other than clear highs and very low temps? 

During December 2010 we had almost 3 weeks of lying snow under both cloudy and clear conditions and freezing fog formed on only one of those nights. It was neither the mildest or the coldest night either.  I see a lot of people mention on forums when looking at certain charts that due to what they see, freezing fog could definitely be a risk. What is it about a particular chart that makes a cold frosty high more likely to produce FF than another?  It would be a great help if anyone could explain the partiuclar conditions that create the right sort of environment for FF to occur locally. Does it have to do with relative humidity? direction of source of cold air? How moist the ground is? 

Thank you for any helpful explanation.

freezing fog.jpg

Interesting question and one I'd like to know the answer to as well, but looking back at occurrences of freezing fog in my locale, particularly in December 2007, December 2008/January 2009, January 2011 and December 2016/January 2017, they all occurred when there was an anticyclone overhead but pressure was moderately high, rather than really high. All occurred between 1020-1030mb. Perhaps pressure too high has an effect on moisture content in the air... can't be sure, but that's a general observation.

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9 hours ago, MP-R said:

Interesting question and one I'd like to know the answer to as well, but looking back at occurrences of freezing fog in my locale, particularly in December 2007, December 2008/January 2009, January 2011 and December 2016/January 2017, they all occurred when there was an anticyclone overhead but pressure was moderately high, rather than really high. All occurred between 1020-1030mb. Perhaps pressure too high has an effect on moisture content in the air... can't be sure, but that's a general observation.

Thank you and that's a really good start. Its such an elusive weather phenomenon but one I love more than snow! Interesting observation about the moderate pressure reading as opposed to intense highs. I suspected it would have something to do with the pressure. Thanks 

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Freezing fog has been a rarity here in recent years, high pressures have often brought clear skies but little fog, I think moisture content may have something to do with it. Sometime we have freezing fog when a layer of cold dense air sits underneath saturated milder uppers higher up, this can occur at the boundary of a frontal feature usually warm front moving into high pressure, the cold layer is then mixed out from above, a slow thaw can happen.

 

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