For decades, the U.S. power system treated extreme heat as a tail risk, managed through seasonal readiness—something for which to prepare. But hotter conditions are now arriving earlier and lasting longer, prompting system planners and grid operators to treat extreme heat as a design baseline—an assumed operating condition.
The U.S. Energy Information Administration’s (EIA’s) May 2026 Short-Term Energy Outlook, for example, projects roughly 1,610 cooling degree days (CDDs) nationwide this year—the standard industry measure of air-conditioning demand—4% above 2025, with the third quarter alone running 8% above the same period last year and 5% above the ten-year average. The North American Electric Reliability Corporation (NERC), the bulk power system’s designated reliability entity, has begun flagging the overlap of early-summer heat with spring maintenance outages as a recurring concern, alongside wide-area heat events that NERC names as a primary reliability risk for summer 2026, on par with generator outages and fuel supply.
Yet every concern about extreme weather appears rooted in the grid’s overall health—particularly its physical fabric: whether existing wires, transformers, and substations can withstand hotter conditions on top of the soaring load growth and aging infrastructure already straining the system.
Among several adaptive measures of note, utilities are now rating their transmission lines hour by hour against ambient temperature rather than against the once-a-season nameplate values they used for decades. High temperatures, meanwhile, threaten to accelerate wear on distribution and substation transformers, aging assets already in short supply and difficult to replace. On a larger systems level, operators are bracing for peaks that now arrive later in the evening, after solar output diminishes. Utilities are also tracking insulator faults hundreds of miles downwind of any fire line, where wildfire smoke deposits conductive particulates on high-voltage equipment, which raises fault risk on otherwise clear days.