Similarly, if visitors go back to their hotel for a longer than average midday break, that impacts calculations. If temps top 90 degrees around noon and don't drop below 90 until 5 pm or below 85 until 8 pm, that leaves a good chunk of the day when the parks are pretty quiet. If someone is at home watching attraction wait times during the 30-40% of the day when visitors are in the pool or hotel room, they will be misled.
As I mentioned up thread, MK reservations for August 29 have been full for close to a month. Until this week, the only other day between now and Thanksgiving when there are no reservations is Halloween. It was pretty clear that there was a lot of demand to visit the parks this past Friday. The heat and humidity impacted the time when guests (both local as well as out of town visitors) felt comfortable entering the park.
It is the etc that impacts a guest's experience. It is the number of people in the stores, lines for food & snacks, for characters, pin trading, PhotoPass, restrooms, City Hall, and the general difficulty just walking around the parks.