The West is baking again as a heat dome is parked over the Intermountain West and Plains where daily highs pushed into the 100s and 110s across California, Nevada, and the interior Northwest this past week. CAISO load answered the call where system peak load (Hour Ending 20, the 7 to 8 p.m. window) climbed from 37,126 MW on Monday to a weekly high of 43,381 MW on Wednesday, July 15, before easing back toward the mid-30,000s over the weekend as a brief cooling trend moved through (Figure 1). CAISO has not needed to call a Flex Alert yet, but with Fresno and the Central Valley flirting with the mid-110s and Death Valley pushing toward 130°F, the margin for error is thin.

Figure 1 | CAISO System Peak Load (HE20), July 13-19, 2026

That is the familiar half of this week's story: hotter weather, more air conditioning, higher peak demand. The less familiar half is happening 1,500 to 2,000 miles east, and it is coming from the supply side instead of the load side.

A Different Kind of Cloud

While the West is hot, the eastern half of the country is dealing with the opposite problem: a historic wildfire smoke event that is dimming the sun rather than intensifying it. Fires that broke out in and near Minnesota's Boundary Waters in early July have burned more than 50,000 acres with little containment, and the Minnesota Pollution Control Agency has issued some of the most severe air quality alerts the state has ever recorded. Smoke from that event, layered on top of ongoing Canadian wildfire activity, has been drifting across the Upper Midwest and into the Northeast for the better part of two weeks.

MISO has felt this on the supply side in a very concrete way: forced and derated capacity across the footprint troughed near 10,745 MW on July 8 and has climbed nearly every day since, reaching roughly 12,875 MW by July 16, an increase of almost 20%, with the sharpest single-day jump landing exactly when the smoke arrived in earnest on July 14 and 15. Some of that is heat stress on thermal units, but the timing lines up closely enough with the smoke's arrival that the two are difficult to fully separate.

NYISO and ISO-NE are seeing a cleaner, more direct version of the same problem, lost solar output. ISO-NE has said thick smoke can cut regional solar production by up to 40% on the worst days, and this week's Canadian smoke plume over New England pushed residential and utility-scale solar arrays well below their normal clear-sky output, even at high summer sun angles. It is a repeat of the pattern first documented in the summer of 2023, when Canadian wildfire smoke drifted into the Northeast and NYISO's day-ahead solar forecasts significantly overpredicted actual output because the forecasting models were not built to account for aerosol loading of that severity.

Figure 2 | The New Era of Smoke-Filled Skies

That 2023 episode is exactly why this week matters beyond the immediate megawatts. NYISO's own day-ahead models have historically explained only about half of the variance in solar output during severe smoke (an R² near 0.50 in post-event research), which means the operational forecast error during smoke events can run well beyond what a normal cloudy day would produce. When that forecast miss lands in the same week as elevated cooling load and thermal outages, it compounds rather than offsets.

Two Coasts, One Grid Stress, Different Levers

The useful way to read this week is to study in contrasts rather than a single story. In the West, the stress is almost entirely demand-side: clear skies mean CAISO's solar fleet is producing close to its full potential right through the peak, so the operational lever is managing load, imports, and battery discharge timing as the net-load curve steepens into the evening. In the MISO and NYISO footprints, the stress is running the other way: smoke is suppressing supply from a resource that operators increasingly count on to shave the mid-day peak, which means more reliance on thermal and import capacity precisely when some of that thermal fleet is also derated by the heat.

Neither event is expected to be structural. CAISO's own summer assessment has flagged extreme heat and wildfire risk as tracked but manageable threats for the 2026 season, and MISO's multiday operating margin forecast already shows derated capacity easing back down as both the smoke and the heat are expected to lift over the coming week. But the juxtaposition is a reminder that “heat risk” and “solar risk” are no longer separable questions for portfolio and reliability planning. A grid can be stressed by too much sun and heat in one region and too little usable sun in another, in the same week, for entirely different physical reasons.

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