I am not remotely a climate change scientist but the way I understand it, it's the *ocean* temps that are rising in regards to global warming...not the weather temps in general.
And the idea is it's causing more extremes in temperature and weather is doing strange things we're not used to. An increase in extreme weather events (tornadoes, hurricanes, drought) In this case, places experiencing extreme cold fronts.
I know Phoenix is getting hotter every year, but I'm pretty sure that has much more to do with an ever-increasing surface area of hardscape (cement, roads, buildings) that cool off much more slowly than the surrounding desert.
We have a major urban heat island here. It's one of the reasons the surrounding suburbs get big thunderstorms but Tempe only got 3.5 inches of rain last year (and I bet my house got less than that).