Sunny 16 works well in most mid latitude areas, even in low latitude areas.

During the Winter in Rochester New York, it is Sunny 11 or Sunny 8. Why, because the color of the sky in the Winter in Rochester New York is the standard for the 18% middle gray card! That is one of the two reasons George Eastman founded Kodak in Rochester. The other reason is that Rochester New York is the World's Largest Natural Darkroom!