With all the cold weather in the southern USA, I am getting an American cold front down here
Readings from my back yard weather station it is cool enough that if I just run my fresh air intake it keeps my home down around 74 degrees to counter act any internal gains and the minimal effect from the sun today.
Probably could count the number of days per year that I can do this on one hand and have some spare fingers to count.
People seem to think you only need to run the cooling in homes when it is 75 degrees or warmer outside.
So a day like this yes I could just open windows.
Down here it does not really matter how hot it is outside, what matters is how humid it is and how sunny it is.
The outside air temperature does not have that much effect on the cooling load, except for the sensible gain of ventilation air or infiltration.
Heat through the walls, the roof is not even based on outside air temperatures like it is when you size a furnace, it is corrected for a value that compensates for sun beating on the walls and the roof.
Its overcast and still has the sun radiating about 58 Btu/hr/sqaure foot on flat surfaces