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      It TMs hard to be blue when the sky is too

      Blue Sky
      Some blue skies are bluer than others and yes there are reasons for this.Recently, a local photographer asked me if I could forecast when the skies would be their bluest.As with many forecast parameters this can be a bit tricky but there are certain conditions that will lead to those crystal clear, deep blue hues.The best environment for blue skies is high pressure and dry, clean air through a deep part of the atmosphere. Generally we can get these conditions soon after a cold front passage.Relatively dry air is important through a deep part of the troposphere for really blue skies. A low relative humidity in the troposphere reduces condensation above us and reduces the white hue that will soften a blue sky.Clean air above us also helps produce a lustrous blue sky. This is simply because air with less particulate matter will be clearer and allow us to see the sky even better. The air contains particulates like smog, sea salt, pollen and dust. Particulates will make the sky appear milkier and will decrease the visibility.A passing cold front from inland many times will give us all the ingredients needed for vibrant blue hues overhead.Generally behind a cold front we will have high pressure and a northerly component to our winds. Northerly winds bring drier air from the continental US as opposed to the Atlantic or Gulf of Mexico. The high pressure behind the front will also produce sinking air and will inhibit cloud formation and condensation.The colder months are when we see the majority of cold fronts make it this far south. During the summer months there is more moisture in the air and we will also, on many days, see a "sea breeze" that can progress into Southwest Georgia which can dull the bluest skies. The sky appears its deepest blue when the air is dry and clean. Water vapor and dust scatter all colors of light, causing the blue to appear washed-out and pale. Why the sky is blue is a whole other topic. For now I give you this poem.BLUE SKYOn days like this, and I know I doYou may just wonder what makes the sky blueIt TMs really quite simple but harder to sayIt first was described by the math guy RayleighIt seems like air molecules small as they areWill scatter the light from our nearest starThe shorter the wavelength in the spectrum of lightThe more it will scatter into our eye sightMostly the blue light is scattered aroundAnd that TMs what we see from here on the groundOf course all of this may not be earth shatteringBlue skies are blue do to Rayleigh scatteringMike Morrison