Heat wave peaks as western grids hold; two states extend alerts

The week-long heat wave gripping the western United States peaked on Tuesday with temperatures above 115°F in Phoenix and Las Vegas, straining power grids that nonetheless avoided rolling outages for a third consecutive day.

Three balancing authorities set all-time demand records in the late afternoon. Grid operators credited record battery discharge during the evening ramp, which covered the gap left as solar output fell while air-conditioning load remained near its peak.

Nevada and Arizona extended emergency heat alerts through Friday, keeping cooling centers open around the clock. Forecasters expect the ridge to break down over the weekend as monsoon moisture moves north.