I often use a web site at http://www.cleardarksky.com/csk/
that I have found to be quite valuable in determining/predicting the quality of light over the next 24 hours.
The site was designed for astronomers to predict sky visibility at night, but because it provides information on a 24 hour day, it is equally valuable for photographers working in daylight.
There are over 1500 Clear Sky Clock locations throughout North America. Rather than try to explain it, I suggest you take a look at the site and determine if the information can help you.http://www.cleardarksky.com/csk/