GFS vs ECMWF Demand-Hub Outlook: 2026-06-10 00Z

Executive Summary

The 15-day outlook shows a notable divergence between models, with the GFS forecasting significantly more national cooling demand than the ECMWF. The GFS projects 152.2 demand-weighted Cooling Degree Days (CDDs), compared to 140.8 for the ECMWF. This ~11.4 CDD difference is primarily driven by a much hotter GFS solution in the key Eastern and Southern hubs beyond the first week of the forecast.

Hub-Level Weather

The national demand picture is driven by the two largest hubs, the Midwest (Chicago, 35% weight) and the East (New York City, 30% weight).

• East (New York City): This hub is the primary source of model disagreement. The GFS forecasts a cumulative 168.5 CDDs, a substantial 21.0 CDDs more than the ECMWF's 147.5 CDDs. The largest divergence occurs in the latter half of the period (June 22-24), where the GFS is consistently 5-8°F warmer.
• South (Atlanta): The GFS is also significantly warmer here, projecting 193.8 CDDs versus the ECMWF's 173.2 CDDs. This ~20.6 CDD gap is most pronounced from June 13th through June 16th.
• Midwest (Chicago): The models are in closer agreement here, with the GFS at 99.9 CDDs and the ECMWF at 95.7 CDDs. Unlike in the East, the ECMWF is slightly warmer than the GFS in the Day 8-15 range.
• South Central (Houston): Both models show strong, persistent heat. The GFS is moderately warmer, with 263.8 CDDs compared to the ECMWF's 252.2 CDDs.

Demand Implications (Natural Gas)

The forecast points to robust cooling demand for natural gas-fired power generation throughout the 15-day period.

• GFS Scenario: The hotter GFS solution implies a stronger call on natural gas for power burn, particularly in the Eastern and Southeastern markets. This would exert upward pressure on regional cash prices in hubs serving PJM and the Southeast.
• ECMWF Scenario: The cooler ECMWF outlook suggests more moderate, though still significant, cooling demand. The ~11.4 weighted CDD difference between the models represents a material variance in daily gas demand for the power sector.
• Run-over-Run Shift: The models have shifted slightly since the prior cycle. The GFS trended marginally cooler (-1.0 CDD), while the ECMWF trended warmer (+0.6 CDD). This has narrowed the gap between them, a minor stabilizing signal.

Model Agreement & Caveats

Confidence in the overall theme of summer heat is high, but the magnitude of demand, especially in the second week, remains uncertain.

• Convergence: The overall convergence score is high at 0.877, indicating good agreement on the large-scale weather pattern. This score improved slightly (+0.0059) from the previous model run.
• Caveats: The primary divergence between the models emerges after Day 7, which is typical but reduces confidence in the specific temperature outcomes for the latter half of the forecast. The significant disagreement in the high-demand Eastern hubs remains the key watch item.
• Source Limitations: This analysis is based on deterministic GFS and ECMWF runs from Open-Meteo. A review of ensemble model guidance would be necessary to fully assess the range of potential temperature outcomes and forecast uncertainty.