Yes, good comments. I would like to know more about how the sun affects the disc flight.
In Slim's case it's the warming effect of the sun on his beer that affects the flight by causing him to drink less due to the increasing temperature of the brew.
I find the fluctuations in gravity to be the most troublesome. I frequently run into areas where the gravity is a bit stronger near the basket and causes my disc to drop lower than I intended and hit the side. Other times the gravity is less intense and the disc floats as if it were filled with helium right over the top. We need to build a course in an area that is gravity controlled. That is an area where we can be assured that there will be no aggravating fluctuations in gravity.