Sky Harbor reached 115 degrees at 3:05 p.m. Saturday, breaking Phoenix's Aug. 22 record of 113 set in 2011. [1] The extreme heat warning now runs through Aug. 28, with highs forecast at 110 to 115 and — the part that matters for the power system — overnight lows holding above 90. [1]

A desert grid gets its rest at night. Transmission lines carry more current when cool, transformers shed the day's accumulated heat, and air conditioners finally cycle off. A midnight that stays above 90 cancels all three: demand flattens into a plateau instead of a valley, equipment never cools, and stress compounds night over night. Through Aug. 28, Phoenix is not forecast to get that recovery window. [1]

The scale is national. Friday's census of broken records counted 332 across the country, most of them heat marks, with the Southwest supplying a dense cluster. [2] Phoenix's single degree on Saturday looks small in that ledger; sustained nights above 90 are the costlier entry.

No outages have been reported through the first days of the streak. Utilities plan around a plateau like this one with peaker plants and demand response; the streak's length, not its peak, decides whether either lever gets pulled. The test is not the afternoon number everyone photographs. It is 2 a.m., and whether the plateau breaks before the transformers do.

-- DARA OSEI, London