From: blockedofcourse@foo.invalid   
      
   On 11/19/2025 3:33 AM, Liz Tuddenham wrote:   
   > Don Y  wrote:   
   >   
   >> On 11/18/2025 2:39 AM, Liz Tuddenham wrote:   
   >>> Don Y  wrote:   
   >>>   
   >>>> Particularly, cloud cover.   
   >>>>   
   >>>> How can I quantify the extent and "density" (opacity) of cloud   
   >>>> cover?   
   >>>>   
   >>>> And, to make it even more interesting, doing so AT NIGHT, as well?   
   >>>   
   >>>   
   >>> At night the clouds would appear warmer than space, so an infra-red   
   >>> scanning system would give you a picture of the clouds.  I don't know   
   >>> how you would calibrate it, because the apparent cloud temperature would   
   >>> depend on air temperature and IR radiation from the earth.   
   >>   
   >> But the cloud cover wouldn't instantaneously change from observations   
   >> made during the preceding daylight/twilight periods.  I.e., "THIS is   
   >> what cloud cover looks like and THAT is what clear skies look like,   
   >> in the Ir" (assuming both are present)   
   >   
   > In the UK there can be hourly changes in the cloud cover from clear to   
   > 90% cover as 'fronts' are blown across the country.   
      
   Of course!  But, I'm not just checking the skies once a day, etc.   
   I will be watching continuously.   
      
   During daylight hours, it is possible to determine which parts of   
   town are seeing "daylight", "cloudy", "precipitation" and virga.   
   My concern isn't with "those areas" but, rather, whether or not   
   the "sky" will shift to bring those conditions to *me*.   
      
   > I think you might have to measure daylight and darkness observations   
   > differently.  The apparent temperature of the clouds will increase when   
   > they are in sunlight - but so will the apparent temperature of the space   
   > in between them, which is filled with illuminated dust particles.   
      
   But, during daylight, I can distinguish between blue skies and white/grey   
   clouds.  I don't have to use the same wavelengths for all my observations.   
      
   >> Think about how "you" can tell the condition of the skies without   
   >> even looking upward:  "It's not *bright* enough for 1PM" or "The light   
   >> is the wrong 'color'"...   
   >   
   > Recently I haven't even needed to look out the window to guess at the   
   > weather.   We had a period of several days of continuous thick black   
   > cloud cover when the ambient light level was so low I needed to switch   
   > on lights to see around the house.   If you are only interested in the   
   > oveall cloud cover, rather than mapping the clouds, an ORP12 and a 1.5v   
   > battery would work in daytime.   
      
   I can look at the "ground" to determine the *type* of cloud cover and   
   whether it is transitional or not.  But, that won't tell me what's   
   on either side of my bit of sky.  It won't help me *plan*.   
      
   --- SoupGate-Win32 v1.05   
    * Origin: you cannot sedate... all the things you hate (1:229/2)