It’s not exceedingly rare but, it’s also not everyday we get a nice dark sky that we can use as a background for something in full sunlight.
It usually means there is a squall coming or maybe a thunderstorm. Either way it makes a great photo op. This creates a nice natural tonal separation between the subject and the background. If we think of this in terms of ‘stops,’ the sky here is a good 3-4 stops darker than the white building and is immediately adjacent so we have a strong line between light and dark.
Even with this difference in exposure values, there is still a wee bit of texture in the dark clouds and a fair bit of blue. That’s some nice latitude.
Of course, dark skies like this are unpredictable and uncooperative but they are fun when you can catch them.