Thanks, Don. I agree there's a UHI component as well, but it's not impacting the trends. Whereas Phoenix has warmed at about .6F/decade since 1896, NCEI has the State of Arizona warming at about a third of that rate (0.2F/decade), so it's not like they are just using Phoenix numbers to calculate the official trends and departures.
By the way, Death Valley - with a population of, checks notes, zero - has 4. But really 6, as the numbers for November & December in 1913 & 1914 are clearly erroneous. The huge surpluses were driven by implausibly high temperatures with impossibly small diurnal ranges that make zero sense in winter in Death Valley. Ignoring those months, it's 6 of 12.