In mid-December 2025, a powerful winter storm accompanied by an Arctic cold outbreak affected much of the central and eastern United States between December 13–15. A strong surge of frigid air spread southward from Canada, producing widespread below-zero temperatures (°F) and heavy snowfall in several regions. The storm system brought significant snowfall across the Midwest, Mid-Atlantic, and Northeast before moving into Atlantic Canada.
In the Upper Midwest, cities such as Minneapolis–Saint Paul saw morning lows near −10 °F, while Fargo, North Dakota reached approximately −29 °F. Other cities, including Milwaukee, also experienced prolonged sub-zero conditions. Farther east and south, parts of the Midwest, Mid-Atlantic, and Southeast were impacted by unusual cold, with advisories extending from eastern Georgia through the Carolinas. California, however, was largely unaffected by this Arctic frontal outbreak.
This cold wave, driven by a disrupted polar vortex that funneled Arctic air unusually far south, created one of the coldest early December periods in years and significantly stressed electricity systems across the United States. Electricity demand surged across every major ISO except CAISO, and throughout the event Enverus consistently delivered lower daily, on-peak, and peak hour MAPE than the ISOs, demonstrating superior system stress forecasting performance.
PJM
Demand in PJM remained below 120 GW from December 10–13 before rapidly rising as the cold wave intensified. Demand fell to 98 GW early on December 14, then climbed sharply through December 15, ultimately exceeding 135 GW. As temperatures moderated, demand fell below 100 GW by December 17.
As exemplified below, Enverus outperformed PJM forecasts, including peak hour performance during the highest stress intervals.
Notably, on Friday, Dec. 12, Enverus’ load forecast projected a Monday peak of roughly 133 GW—outpacing the ISO’s 126‑GW estimate and demonstrating more accurate peak‑load prediction three days in advance.
ERCOT
Texas exhibited a similar trend, with a sharp morning peak on December 15, followed by a rapid drop on December 16 as temperatures rebounded.
Enverus delivered significantly lower daily, on-peak, and peak hour MAPE compared to ERCOT.
MISO
MISO saw an unusually high Sunday afternoon peak on December 14 due to extreme temperatures, followed by strong morning peaks on December 15.
Enverus consistently produced lower MAPE than MISO throughout the cold snap, even during the most volatile periods.
Image 3. Enverus Mosaic proprietary platform (data displayed in Hour Beginning), evolution of MISO’s load forecast and Enverus load forecast from December 14 to December 16, 2025.
SPP
SPP demand peaked on December 15, with December 14 demand notably higher than December 16, reflecting the sharp temperature swings across the region.
Again, Enverus maintained lower daily and on-peak MAPE across all days evaluated.
NYISO
NYISO demand did not exhibit a morning peak on December 15, instead experiencing an evening spike later that day. Demand on Sunday, December 14, was significantly higher than on Saturday, while Monday morning demand remained just below Sunday’s peak. These patterns illustrate the impact of plunging temperatures.
Enverus delivered substantially lower peak hour MAPE, demonstrating superior responsiveness to rapidly shifting load patterns.
ISO-NE
In a similar vein to NYISO, ISO-NE did not experience a morning peak on December 15 but instead saw an evening peak with volatile conditions continuing through December 16.
Enverus achieved lower daily and on-peak MAPE across both days, demonstrating strong performance in complex northeastern weather patterns.
Delivering Confidence in High‑Volatility Power Markets
Across PJM, ERCOT, MISO, SPP, NYISO, and ISO-NE, Enverus consistently outperformed ISO load forecasts during one of the most severe early winter cold events in recent history. The one-day-ahead Enverus forecasts demonstrated tighter alignment to real-time system behavior, lower error rates, and higher reliability during rapidly changing temperature conditions.
These results highlight the strength of the Enverus Mosaic forecasting platform, which continues to deliver exceptional performance under both routine and extreme grid conditions.
About Enverus Power and Renewables
With a 15-year head start in renewables and grid intelligence, real-time grid optimization to the node and unparalleled expertise in load forecasting that has outperformed the ISO forecasts, Enverus Power and Renewables is uniquely positioned to support all power insight needs and data-driven decision making. More than 6,000 businesses, including 1,000+ in electric power markets, rely on our solutions daily.
