An intense heat wave made its way across the middle of the country earlier this week delivering high demand and high prices in MISO. The well-above normal temperatures strengthened over the weekend. Demand, which had yet to reach 100 GW this June at the start of last week, was now peaking over 110 GW. Over the weekend, wind generation was strong throughout both days, averaging close to 20 GW in a steady and flat profile. Meanwhile, MISO’s growing solar capacity was providing more than 12 GW in the middle of the day. As the wind forecast for Monday solidified, however, the grid operators knew they would be in a tight spot. Forecasts for demand on Monday night had a peak over 120 GW while the wind volumes shrunk to under 10 GW in the evening. A Max Gen Warning was declared for Monday night, which ultimately became a Max Gen Event Step 1b. For generators, this meant all available resources should be turned on and ready. Ultimately, demand came in under forecast, not quite reaching 120 GW, but it was still enough to push real-time prices over $1000/MWh at the Indiana and Michigan hubs.

Figure 1 | MISO Market Summary – Forecasts and Actuals (June 21 – 29, 2025)

The figure below helps show the extremes of both heat and levels of demand in North MISO from this event. Average North MISO real-time demand is plotted against average North MISO temperatures for days in May and June. Green circles are from days in 2025 while green stars show the most recent data (June 20 – 23). Red circles show days in 2024 while orange is data from 2023. This past weekend, shown as the stars far to the right, displays how extreme both the heat and the demand was for the region. Most of the green dots have come above the data from previous years, indicating structural load growth. The combination of load growth plus hotter temperatures has proven to be a tricky combination for the MISO grid to handle and perhaps a warning for what this summer could bring.

Figure 2 | Avg. North MISO Temperatures vs Avg. North MISO

MISO power market flash subscribers got a heads up on Monday while Midwest natural gas flash subscribers got the low down on the heat last week. We’ve also covered the events in our most recent article, titled ‘Heating Up the Evening Ramp Prices’. If you want to stay on top of future events in MISO, you can subscribe to our Enterprise plan which offers access to our market flashes with the most up-to-date and pertinent information.