The seasons come from real weather, not a guess: the 1991–2020 monthly normals recorded at ST GEORGE, UT US, published by NOAA's National Centers for Environmental Information. USC00427516
A cooling degree day counts one degree that a day's average temperature sat above 65°F. This town runs about 2,416 of them a year — that is the number that decides how much of the year the air conditioning is working, and which months carry the cost.
One number here is an estimate rather than a measurement: how much electricity a square foot of cooled floor uses per cooling degree day. It works out to about 0.00091 kWh, and it comes straight from the U.S. Energy Information Administration's 2020 Residential Energy Consumption Survey — the air-conditioning electricity, cooled floor area and long-run degree days reported by the 12.2 million air-conditioned homes in the survey's Hot-Dry climate zone, which is the zone St. George sits in. Those homes averaged 2,749 kWh of cooling a year over 1,396 cooled square feet and 2,068 degree days. The figure carries whatever equipment those homes actually had, which we treat as about SEER 13 — the federal minimum for units sold between 2006 and 2015, and a fair description of the middle of the installed stock. A useful check on the whole thing: this model puts an average-sized St. George home at roughly 330 kWh a month for cooling, and the EIA's own billing figures for the city utility show an average home using 982 kWh a month in total. The two were worked out from different data and they fit.