GFS vs ECMWF Demand-Hub Outlook: 2026-09-10T00:00Z

Executive Summary

The 15-day outlook shows a significant divergence between models, with the GFS forecasting a much warmer, cooling-demand-heavy period than the ECMWF. The GFS projects 123.8 weighted CDDs versus the ECMWF's 92.2, a material difference driven primarily by a hotter forecast in the East and South. Conversely, the ECMWF sees a quicker transition to fall, forecasting 8.2 weighted HDDs versus just 3.3 in the GFS, introducing early-season heating demand in the Midwest and Northeast.

Hub-Level Weather

The primary drivers of the national demand forecast are the high-weighted hubs in the Midwest and East, where the models show their largest disagreements.

• East (New York City): This hub shows the most dramatic split. The GFS forecasts a robust 108.2 cumulative CDDs, while the ECMWF is far cooler at 64.1 CDDs and introduces 8.7 HDDs in the back half of the period.
• Midwest (Chicago): A similar, though less pronounced, theme is present here. The GFS sees 61.1 CDDs and minimal heating demand (0.85 HDDs). The ECMWF is cooler with only 45.6 CDDs and the emergence of 6.4 HDDs.
• South Central (Houston): Both models remain firmly in cooling season, but the GFS is substantially hotter, calling for 312.9 CDDs compared to 247.3 in the ECMWF.
• Northeast (Boston): The models are closer on cooling demand but diverge on heating, with the ECMWF showing more late-period heating load (33.3 HDDs) than the GFS (27.9 HDDs).

Demand Implications (Natural Gas)

The significant model disagreement presents two distinct scenarios for Natural Gas demand.

The GFS outlook would imply a lingering, above-normal power burn for cooling, extending summer demand patterns deeper into September. This would be supportive for NG futures by delaying the typical shoulder-season demand lull.

In contrast, the ECMWF solution signals a more rapid shift toward shoulder season conditions. Its forecast implies significantly lower cooling demand and the first notable signs of residential/commercial heating load in northern markets. This scenario would be less supportive for natural gas prices compared to the GFS.

The latest model cycle showed the GFS trending cooler (-6.1 weighted CDDs) and the ECMWF trending slightly warmer (+1.2 weighted CDDs), indicating a slight convergence, though a major gap remains.

Model Agreement & Caveats

The overall model agreement is moderate, with a convergence score of 0.67. This score improved by 0.0954 from the prior cycle, but the persistent gap between the models, particularly from day 5 onward, warrants caution. The significant difference in outcomes suggests lower confidence in the 15-day forecast.

This analysis is based on deterministic runs from the GFS and ECMWF models via Open-Meteo. It does not incorporate ensemble guidance, which would provide a broader range of potential outcomes. The demand-weighting is a proxy for national consumption and does not capture all regional complexities of the natural gas market.