GFS vs ECMWF Demand-Hub Outlook: 2026-07-31 00z

Executive Summary

The 15-day outlook shows a significant divergence between models, with the GFS projecting a much hotter, higher-demand scenario than the ECMWF. The GFS is +32.5 weighted CDDs above the ECMWF nationally (216.4 vs 183.9), a spread driven primarily by a forecast for intense heat in the East. Run-over-run trends have widened this disagreement, as the GFS added a substantial +25.7 weighted CDDs while the ECMWF trended slightly cooler (-3.2 wCDDs), lowering overall forecast confidence.

Hub-Level Weather

The primary driver of the national forecast difference is the East, supplemented by notable heat in the Midwest and South Central per the GFS.

• East (New York City): This is the epicenter of the model disagreement. The GFS is a substantial 73.7 CDDs hotter than the ECMWF (248.1 vs 174.4) over the 15-day period. The divergence becomes most pronounced from August 6th onward.
• Midwest (Chicago): As the largest demand-weighted hub (0.35), the Midwest shows a meaningful split. The GFS forecasts 15.5 more CDDs than the ECMWF (143.3 vs 127.8), with the largest daily differences occurring in the day 6-10 period.
• South Central (Houston): Both models are hot, but the GFS maintains a hotter edge, forecasting 32.7 more CDDs (353.2 vs 320.5). The difference is largest in the latter half of the forecast.

Demand Implications (Natural Gas)

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

• GFS Scenario: The GFS outlook implies strong, above-normal cooling demand that would be highly supportive of gas prices. The significant heat forecast for the high-population centers of the East and Midwest would drive robust power generation load.
• ECMWF Scenario: The ECMWF presents a more moderate, closer-to-normal demand picture. While still showing consistent summer heat, it lacks the intensity of the GFS, suggesting a more balanced supply/demand environment.

Model Agreement & Caveats

Forecast confidence is currently low due to significant model disagreement and unstable run-over-run trends.

• Model Divergence: The GFS and ECMWF are trending in opposite directions. The GFS added significant demand (+25.7 wCDDs) versus its prior run, while the ECMWF shed a small amount of demand (-3.2 wCDDs). This widening gap is a key indicator of forecast uncertainty.
• Convergence Score: The provided convergence score is 1.0. However, the raw ~32.5 weighted CDD difference between the models indicates this score may not be fully capturing the material forecast risk. The significant spread, especially in the 6-15 day outlook, should be prioritized over the score.
• Source Limitations: This analysis is based on a limited number of hubs and deterministic runs from Open-Meteo. It does not incorporate ensemble guidance, which would provide a more complete view of the range of possible outcomes.