Recent showers and thunderstorms have broken the significant heat wave which was firmly entrenched across the region. So how hot was it during this heat wave? The heat wave started in earnest on July 10th. The tables below show just how hot this period was for Phoenix and Yuma. While it is well known that a significant urban heat island signal has developed over the years in Phoenix (which primarily impacts low temperatures), this heat wave was actually more notable for how extreme the high temperatures were. The average high temperature from July 10-20 in Phoenix was 112.7 °F, the hottest on record for that period. Also of note was how significant this event was for Yuma, especially with respect to the overnight low temperatures.