GFS vs ECMWF Demand-Hub Outlook: 2026-07-25 00Z

Executive Summary

The 15-day outlook shows a significant bullish divergence between models, with the GFS projecting much stronger cooling demand than the ECMWF. The national demand-weighted forecast shows the GFS with 214.8 total CDDs versus 190.2 for the ECMWF, a difference of ~25 CDDs primarily driven by a late-period heat forecast in the GFS. Both models trended cooler compared to the prior cycle (GFS -5.5 CDDs, ECMWF -3.3 CDDs), though the GFS remains the hotter outlier.

Hub-Level Weather

The national GFS/ECMWF spread is driven by key high-demand regions in the second half of the forecast period.

• Midwest (Chicago, 35% weight): The GFS is materially hotter, forecasting 191.8 CDDs versus the ECMWF's 168.5. The divergence is most extreme on Aug 7-8, where the GFS shows intense heat (mean temps in the high 80s) while the ECMWF is far more moderate (low 70s).
• East (New York City, 30% weight): A similar pattern exists, with the GFS (181.2 CDDs) projecting significantly more cooling demand than the ECMWF (158.8 CDDs). The disagreement again peaks in the 10-15 day period.
• South (Atlanta, 10% weight): This hub shows the largest model disagreement, with the GFS forecasting an extreme 319.1 CDDs against a more seasonal 210.9 CDDs from the ECMWF.
• South Central (Houston, 15% weight): Both models show strong, persistent heat, though the GFS is consistently hotter, accumulating 366.6 CDDs to the ECMWF's 326.6.

Demand Implications (Natural Gas)

The forecast implies a period of robust summer cooling demand, with a significant upside risk to power burns if the GFS solution verifies.

• The GFS's forecast for widespread, intense heat across the Midwest and East in the 8-15 day period would translate to substantially higher natural gas demand for power generation than the more moderate ECMWF solution.
• The prior run's trend cooler (-5.5 CDDs for GFS) slightly tempers the demand outlook, but the overall picture remains supportive of above-average demand, especially in the GFS.
• The ECMWF presents a more seasonal demand outlook, suggesting power burns would be strong but not at the extreme levels implied by the GFS.

Model Agreement & Caveats

Confidence in the near term is high, but significant uncertainty exists in the crucial 8-15 day outlook.

• Convergence: The overall convergence score is high at 0.96608, indicating strong agreement on the synoptic pattern in the first 7-10 days of the forecast.
• Divergence: The primary forecast uncertainty lies in the extended range (approx. Aug 3-8), where the GFS builds a significant heat dome over the central and eastern U.S. that is not present in the ECMWF. This late-period disagreement is the source of the large spread in total CDDs.
• Limitations: This analysis is based on Open-Meteo's public model data. Forecasts beyond 7-10 days are subject to large revisions, and the current model spread highlights this inherent uncertainty. The provided hub weights are a proxy for, and not a complete representation of, total U.S. natural gas demand.