This morning, Phoenix hit 51F, just missing the record of 49F last set in 1965. But as I mentioned in my previous post on the record high we hit (just four days ago!), the growth of the Phoenix urban heat island in the last 4 decades has a lot to do with how these records are set and not set.
The Phoenix urban heat island has been measured many times, including by my son in a recent science project. In that project we measured an urban warming of 8-10F around midnight vs. the outlying areas of the city. We have not measured the daytime heat island effect, but others have, such that it is not hard to imagine that the record high set four days ago would not have been a record when the city was smaller. Today, we can similarly argue that we could have easily had a record low last night, since we only missed by 2 degrees, had it not been for the heat island effect. While 2 vs. 8-10 degrees seems compelling, we also had a lot of wind last night that tends to break up the urban heat island effect, so we can never be sure.