According to the National Weather Service, it is officially the second warmest December on record in Tucson. Daytime highs are expected to be in the low 80s in and around Tucson on Saturday, which is 15-20 degrees above our average for this time of year. As a ridge of high pressure moves through Arizona, however, Tucson will experience a "slight" cooling to 78 degrees for a daytime high on Sunday, New Years Eve.
Mostly clear conditions will prevail for Southern Arizona on New Years Eve with temperatures in the low 60s by 8pm. Temperatures will then drop into the low 50s, once you ring in 2018 at midnight. You may want to wear a jacket if you are planning on being outdoors.
You can get your weather any time at kvoa.com.