PJM Heatwave Analysis: Forecasting for 90-degree heat and a new federal holiday

A recent major heatwave swept most of the country with temperatures exceeding 90 degrees F for several consecutive days and setting new records in some areas. PJM really sweat it out, issuing Hot Weather Alerts starting on June 13th. Those Hot Weather Alerts are still in effect 13 days later for the 26th for the Mid-Atlantic and Southern Regions. These extreme temperatures, coupled with a relatively new federal holiday, tested the adaptability of PJM's models in this rapidly changing environment.  

The heatwave began on June17th, with temperatures nearing 90 degrees F for the first time in 2024, resulting in a total load for the day reaching 2,681.2 GWh. Amperon’s projections beat PJM’s with a mean absolute percent error (MAPE) of 0.89% compared to PJM’s 1.13%.

Temperatures continued to rise on the 18th, hitting the inflection point of 90 degrees. Amperon’s forecast of 142.9 GW was only 0.32% off from the actual peak demand of 143.4 GW. However, PJM began a trend of over-forecasting that persisted throughout the heatwave, forecasting 145.7 GW, an error of 1.64%.  

Demand during the PJM heatwave when temperatures reached the 90s. Source: Amperon

The 19th brought novel challenges as the market attempted to forecast peak demand on the relatively new federal holiday, Juneteenth. According to a study done by Mercer, 41% of large employers with 500+ employees were observing the federal holiday and had the day off. Coinciding with the new federal holiday, high temperatures in major cities like Chicago and Philadelphia were forecasted to cross the 90-degree mark. The ISO predicted a peak demand of 146.3 GW, which would have been the third highest demand hour last summer. Demand ended up materializing at a peak of 143.1 GW, 2.79% lower than the ISO's call and 5.26% above the Amperon day-ahead forecast. Amperon’s forecast model overstated the estimated impact of the holiday load reduction. However, the new data will allow Amperon’s machine learning technology to calibrate the model, enhancing its ability to understand and capture the dynamics of this evolving holiday.  

Despite still being in the throes of the heatwave on the 20th, peak demand decreased to 142.0 GW compared to Amperon’s forecast of 143.4 GW, just under 1% over the actual. Meanwhile, the ISO’s forecast remained high at 145.6 GW, exceeding actuals by 2.51%.  

The peak demand for PJM occurred at 6 PM on the 21st, reaching 147.5 GW, just below the ISO forecast and within 1% of Amperon’s day-ahead forecast. Total load on the day reached an impressive 2,858.5 GWh.  

The 22nd brought in the last 90-degree day, and with it a strong total demand at 2,831.7 GWh. PJM continued to over-forecast, however, both the ISO and Amperon’s forecasts were extremely close to actuals with an absolute percent error at the peak HE18 of 0.47% and 0.79%, respectively.

PJM’s propensity to over-forecast persisted beyond the heatwave, extending through the 23rd, with an absolute percent error of 3.31% during the peak HE18, compared to Amperon’s 0.97%.  

Demand has returned to normal June levels, with the week’s PJM forecast in the 2,600 GWh range for the remainder of the month. The recent heatwave might just be a prelude to a scorching summer ahead. According to NOAA, there's a 50% chance that this summer could become the hottest on record and a certainty of it ranking among the top four hottest summers ever. These seasonal projections indicate that we might face several more intense heatwaves in the coming months. This early heatwave serves as a stark warning of potentially extreme temperatures ahead.

Comparing Amperon's day-ahead forecasts to PJM's for the peak hours of the heatwave.
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