In the Phoenix valley, they sell thermometers that go no lower than 50. No point wasting mercury!!!
When I was there, Phoenix was usually 10 degrees hotter than Tucson at any given time, so I'm guessing it never gets cool enough. Tucson sits in a valley surrounded by mountains and one of them, Mt Lemon, has a ski area which gets snow.
So if you ever get curious and are willing to drive two hours in the winter to find out...
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