This chart shows you how much cloud cover there is (the darker the color, the clearer the sky), how much light you’re getting from the moon (Darkness), and even how water vapor in the air (Transparency) and air turbulence (Seeing) will affect your ability to resolve detail in the sky—all broken down into blocks by time.
But the site doesn’t stop with this info. There are a bunch of extra tools at your disposal like a light pollution map, sun and moon data, and a star map. And if you click on any of the colored blocks in your chart, a full map will pop up showing you the expected conditions at that time, overlaid onto the location.
Clear Dark Sky should be a part of every diligent night sky photographer’s location scouting and preparation workflow. Check it out for yourself here.