"Never presume August is a safe or reliable time of year. It is the season of reversals, when birds no longer sing in the morning and the evenings are made up of equal parts golden light and black clouds." Alice Hoffman, from the book 'Practical Magic,' one of my favorite books by one of my favorite authors.
This is an area on Highway 18, just as you're coming into Rim Forest. You can see this from the turnout at Red Rock Wall (although you need a good zoom lens), and sometimes the light there is spectacular.