GFS vs ECMWF Demand-Hub Outlook: 2026-07-06T00:00Z

Executive Summary

The 15-day outlook shows a significant divergence between models, with the ECMWF forecasting much stronger cooling demand than the GFS. The ECMWF projects 217.2 demand-weighted Cooling Degree Days (CDDs) versus the GFS's 175.8, a material difference of 41.4 CDDs. This disagreement is driven primarily by a much hotter ECMWF solution in the high-demand Midwest hub, particularly in the Day 8-15 period.

Hub-Level Weather

The national forecast difference is almost entirely attributable to conflicting outlooks for the Midwest and East.

• Midwest (Chicago): This is the main point of divergence. The ECMWF is dramatically hotter, accumulating 227.1 CDDs over the 15-day period, while the GFS forecasts only 128.5 CDDs. The split becomes extreme from July 13th onward; for example, on July 16th, the ECMWF forecasts 24.3 CDDs versus just 5.0 CDDs from the GFS. As the highest weighted hub (0.35), this difference is the primary driver of the national total.
• East (New York City): The ECMWF is also notably hotter in this key hub (0.30 weight), projecting 190.0 CDDs compared to the GFS's 158.7 CDDs. The disagreement grows in the latter half of the forecast window.
• South Central (Houston): In contrast to other regions, the GFS is the hotter model in the South, forecasting 314.3 CDDs in Houston versus 277.9 CDDs from the ECMWF. This provides a partial bearish offset to the GFS's cooler outlook elsewhere.

Demand Implications (Natural Gas)

The conflicting model solutions present very different scenarios for natural gas power burn over the next two weeks.

• ECMWF: The hotter solution, particularly in the population-dense Midwest and East, implies robust and sustained cooling demand, which would be bullish for gas-fired power generation.
• GFS: This forecast suggests a more moderate demand picture, with significant late-period cooling focused more on the South Central region.
• Run-over-Run Trend: Both models trended cooler compared to their prior 12Z cycle. The GFS showed a significant bearish shift (-12.1 weighted CDDs), while the ECMWF trended only slightly cooler (-3.5 weighted CDDs), suggesting some momentum toward a less intense heat dome scenario.

Model Agreement & Caveats

Confidence in the 15-day forecast is low due to the significant model disagreement, especially beyond the first week.

• Convergence: The provided convergence_score of 0.9986 is misleadingly high, as it is based on Heating Degree Day (HDD) agreement, which is irrelevant during peak summer. The substantive disagreement is in CDDs, where the models are far apart.
• Caveats: The primary uncertainty lies in the Day 8-15 period in the Midwest. Until subsequent model runs show better agreement on the pattern evolution in this key demand region, the long-range demand signal should be treated with caution.
• Source: This analysis is based on raw GFS and ECMWF model output from Open-Meteo and does not include any proprietary blending or post-processing.