Interesting. I was in Wyoming and noticed this as well. During the partial eclipse it was impossible to tell that the sun was dimming except that I could measure this with my camera's light meter. My friend hardly believed me when I informed her the sunlight had been halved three times (losing three stops) -- except that we could feel this difference in how chilly it had become. It is only as the last bit of sun is obscured that the world goes dark in any noticeable way.