Is the high Phoenix heat in the movie ‘Psycho’ accurate?

Dear Tom,
Watching the movie “Psycho,” I noticed the opening credits show the setting as Dec. 11 in Phoenix, yet the characters complain about the excessively hot weather. Does December ever get hot enough in Phoenix to require air conditioning?
— Mike Beirl, Bolingbrook
Dear Mike,
It does, though December weather that hot would be the exception and not the rule. Typical December high temperature in Phoenix averages in the middle and upper 60s, but a check of weather records dating back to 1896 indicates that more than half of the month’s 31 days have reached the 80s with the month’s record highs ranging from 77 on Dec. 21, 1985, to 87 on Dec. 10, 1950. Considering that triple-digit highs are the norm in Phoenix from June into September, temperatures in the 80s don’t seem that hot, but air conditioning use would not be that unusual.

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