GFS vs ECMWF Demand-Hub Outlook: 2026-05-25T00:00Z

Executive Summary

The 15-day outlook shows significant model disagreement, with the GFS projecting a much stronger weather-driven demand scenario than the ECMWF. The GFS forecasts a total of 130.9 weighted degree days (25.5 HDD, 105.4 CDD) compared to the ECMWF's 105.8 (18.5 HDD, 87.3 CDD). This divergence stems from conflicting solutions for a cool air intrusion, with the GFS driving it into the Midwest while the ECMWF places it over the Northeast, resulting in low overall forecast confidence.

Hub-Level Weather

The national forecast is driven by major disagreements in the two largest demand-weighted hubs:

• Midwest (Chicago, 35% weight): This is the primary point of contention. The GFS model forecasts a significant late-season cold shot from May 28 - June 2, accumulating 38.8 HDDs. The ECMWF, in stark contrast, keeps the region much milder, forecasting only 1.6 HDDs over the entire 15-day period.
• East (New York City, 30% weight): The models show the opposite scenario here. The ECMWF is substantially colder, particularly from June 1-4, accumulating 33.5 HDDs for the period. The GFS is much warmer, forecasting only 14.3 HDDs and significantly more cooling demand (95.7 CDDs vs. ECMWF's 55.6 CDDs).
• South Central (Houston, 15% weight): Both models show consistent cooling demand, but the GFS is materially hotter throughout the forecast, projecting 222.1 cumulative CDDs versus 178.1 for the ECMWF.

Demand Implications (Natural Gas)

The conflicting forecasts imply very different outcomes for shoulder-season natural gas demand.

• GFS Scenario: The GFS suggests a high-demand "whiplash" pattern. It blends strong cooling demand in the South and East with a notable burst of late-season heating demand in the high-consumption Midwest region. This combination of both HDD and CDD accumulation would be bullish for natural gas demand compared to seasonal norms.
• ECMWF Scenario: The ECMWF presents a more moderate, regionally split picture. It points to heating demand being confined to the Northeast, while the rest of the country sees mild to warm conditions. This would result in a lower national demand footprint than the GFS.

The run-over-run trend shows the GFS shifted dramatically warmer (+32.6 weighted CDDs, -14.9 weighted HDDs), amplifying the total demand forecast. The ECMWF also trended warmer (+13.1 weighted CDDs) but to a lesser extent.

Model Agreement & Caveats

Confidence in this forecast is low.

• Convergence: The model convergence score is poor at 0.318, indicating significant disagreement on the evolution of the weather pattern beyond the first few days. The score has worsened since the prior cycle (delta +0.056), meaning the models are diverging, not converging, on a solution.
• Caveats: The primary uncertainty is the placement and intensity of a trough moving into the eastern half of the U.S. around days 5-10. Until the models come into better agreement on this feature, the demand outlook, particularly for the Midwest and East, should be viewed with extreme caution.
• Source Note: This analysis is based on single-point locations for major hubs provided by Open-Meteo. It serves as a directional index and may not perfectly reflect broader, population-weighted regional demand.