Chinook Posted December 1, 2011 Share Posted December 1, 2011 I don't believe I have seen frost or dew form with a wind over 10mph. Is there some physical reason why frost or dew must form with a very light wind? I believe the surface must be colder than the surrounding air. I am not sure how much colder it must be for a visible frost or dew formation, but let's say 2-3 degrees F. I think the wind usually mixes up the air right next to the ground, perhaps taking away the possibility that objects are 2-3 degrees F colder than the surrounding air. Is that correct? Or is it still possible for objects to be colder than the surrounding air with wind? Link to comment Share on other sites More sharing options...
isohume Posted December 1, 2011 Share Posted December 1, 2011 I don't believe I have seen frost or dew form with a wind over 10mph. Is there some physical reason why frost or dew must form with a very light wind? I believe the surface must be colder than the surrounding air. I am not sure how much colder it must be for a visible frost or dew formation, but let's say 2-3 degrees F. I think the wind usually mixes up the air right next to the ground, perhaps taking away the possibility that objects are 2-3 degrees F colder than the surrounding air. Is that correct? Or is it still possible for objects to be colder than the surrounding air with wind? That's correct. Higher winds mix warmer air just above the sfc to the sfc. So on a calm night you could have 37 F at the sensor level and have frost...while on a relatively windy night you could have 37 F and no frost formation. Assuming similar sfc-based moisture in both cases. Link to comment Share on other sites More sharing options...
HoarfrostHubb Posted December 4, 2011 Share Posted December 4, 2011 But you don't typically see frost forming even on a cold night (air 29F for example) if there is a decent wind... Any reason? Link to comment Share on other sites More sharing options...
isohume Posted December 4, 2011 Share Posted December 4, 2011 But you don't typically see frost forming even on a cold night (air 29F for example) if there is a decent wind... Any reason? There has to be enough llvl moisture. Ie: a temperature/dewpoint spread of 3 degrees F or less at sensor level is one of the criteria we use to gauge a frost potential. If the wind is high enough, which it usually is with a colder air mass pushing in...it will trump any high end moisture and not allow frost to form. It does this by mixing drier air aloft to the surface...as caa creates downward motion and it becomes more turbulent as it nears the sfc. Link to comment Share on other sites More sharing options...
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