MISO cautioned it likely is in for heat waves and drought this summer with a slight chance it navigates a 130-GW peak in July.

The RTO expects a coincident summertime peak of 122.6 GW, exactly the same as for July 2024. However, based on its load-serving entities’ noncoincident peak forecasts, MISO reported load could drift up to 130 GW in July, a high never seen in the footprint.

In MISO, noncoincident peak forecasts represent the monthly peak load submitted by LSEs; coincident peak forecasts, on the other hand, are adjusted relative to the RTO’s seasonal peaks.

According to LSEs’ noncoincident peak forecasts, MISO could contend with a 127.6-GW peak even in August.

MISO’s all-time summer peak of 127 GW occurred July 20, 2011. Last summer, it also warned it might eclipse that record but rounded out the season with a 122-GW peak in late August. (See MISO: Hurricanes, Heat Wave Noteworthy Against Relatively Peaceful Summer and MISO Braces for Hot Summer, Potential 130-GW Peak.)

During a May 8 summer readiness workshop with stakeholders, MISO noted it will have more capacity than absolutely necessary when its planning year begins June 1.

The grid operator set an initial planning reserve margin requirement of 135.2 GW for summer and ended up clearing slightly over 137.5 GW because of its sloped demand curve in April’s capacity auction, the first time the curve was used. It is meant to procure more capacity than strictly necessary to meet MISO’s one-day-in-10-years loss-of-load standard. (See MISO Summer Capacity Prices Shoot to $666.50 in 2025/26 Auction.)

MISO’s total cleared capacity includes 124.2 GW of traditional generation and 13.3 GW of load-modifying resources, which include demand response, behind-the-meter generation and energy efficiency. The RTO must declare an emergency to access its LMRs. Even if MISO realizes its most likely outcome of a 123-GW peak, the demand will require nearly all of its nonemergency resources.

When asked by stakeholders whether MISO could place a probability on entering emergency procedures, resource adequacy engineer John DiBasilio pointed out that it “cleared more resources than usual” for the 2025/26 planning year and said those resources are under an obligation to offer.

“You are gaining a mandate on some additional resources to be available in the market,” DiBasilio told stakeholders. He declined to guess the likelihood of MISO declaring an emergency.

The RTO said its 13-GW solar fleet, which has more than doubled in size since last summer, also should help. MISO meteorologist Adam Simkowski said it expects to have nearly 15 GW in solar capacity by July, which will translate to an average 9-GW daytime high. However, Simkowski warned that solar output is more challenging to forecast minutes ahead in the real-time market than wind generation, which has more predictable forecasts.

Simkowski said by August, solar contributions should be consequential enough to shave evening peaks and delay usual net peak loads by two to three hours. Because solar output tapers in the evening, MISO will have greater ramping needs, “a relatively new phenomenon” it must contend with, Simkowski said. The RTO said it plans to introduce dynamic reserve requirements that can be set to high, medium or low based on forecasts and weekday versus weekend use patterns.

MISO previously said it hopes to use dynamic reserves by the beginning of 2026. The Independent Market Monitor has warned that ramping needs beyond 10 GW are becoming increasingly common in the footprint and presenting challenges in the control room. (See MISO IMM Warns of Operational Difficulties with Growing Solar Fleet.)

Heat and Drought

Simkowski and fellow meteorologist Brett Edwards said they expect temperatures to trend above normal in summer, with the potential for drought over the Central U.S. to exacerbate heat waves in MISO.

They said MISO South, especially areas along the Gulf Coast, should experience more normal precipitation patterns.

The RTO said five historical years (2012, 2017, 2018, 2021 and 2022) provide the best reference for what is likely to happen. It said all analog years had summers in which load topped 115 GW systemwide, with 2012’s persistent heat and extreme drought delivering load that exceeded 120 GW for multiple days.

Edwards said the footprint might be in for a repeat of summer 2012, where load and heat were high.

MISO said over summer 2024, temperatures lined up with historical averages, and only two days in late August exceeded a 90-degree Fahrenheit systemwide temperature. The RTO is not expecting such tame temperatures this year.

The 2025 outlook lines up with the National Oceanic and Atmospheric Administration, which has called for above-normal temperatures over the whole of the continental U.S. and below-normal rainfall across most of the MISO footprint.

Finally, MISO said it anticipates a normal to slightly busier-than-usual hurricane season in the Atlantic Ocean, with an early start time similar to 2024 because of warm ocean waters in the Caribbean.