As the fall season progresses, the average percent of possible sunshine decreases due to an increase in the frequency and duration of fog and low overcast. There are several reasons for this:
Lowering sun angle. On Oct. 23, the peak elevation of the sun above the southern horizon at solar noon is 35.8 degrees. As the sun angle lower further, incoming solar radiation may be too weak to penetrate and dissipate low cloud or fog layers.
Lengthening nights. On Oct. 23, the duration from sunset to sunrise is 13 hours, 15 minutes. As nights lengthen, surface temps have a longer time to lower resulting in an increased frequency of fog.
Relatively warm water. As air temps drop, moisture flux from neighboring lakes and rivers is more likely to initiate fog formation.
