Wow! This is insane. The sun has been up for an hour, and there is still frost on the north facing roofs around, and in my yard in the shade. The high here yesterday was 57 and the low this morning was 30. These are temperatures like we normally see only in January, and then only when a major winter storm comes through. Just a few days ago it was in the 80s, the glorious fall weather that we get in Phoenix, clear skies with an occasional puff of cirrus.
It's strange. The first frost in this part of Phoenix used to be after the middle of December, if it came at all. I remember years without a frost at all, though none recently. The last few years, the first frost has been at the beginning of December, and there have been lots of frosts. I think it is because it is getting drier, so there is more radiative cooling. Now this. The deciduous trees haven't even lost their leaves, and the citrus is still in growth stage.
The official temperature is higher. It is accurate only for the micro climate around the official Phoenix weather station near the airport. There is a lot of city in every direction from there, and it also is more humid, since there is a lot of flood irrigation in those older parts of the city that used to be agricultural. The Salt River probably drains cold air away from the area, as well.