GFS vs ECMWF Demand-Hub Outlook: 2026-07-28 00Z

Executive Summary

The 15-day outlook presents a significant model disagreement, with the GFS forecasting a much hotter and more demand-intensive period than the ECMWF. This divergence is driven primarily by the high-demand Midwest and East hubs, particularly in the 8-15 day range. The GFS trended substantially hotter (+36.6 weighted CDDs) versus the prior cycle while the ECMWF trended cooler (-15.5 weighted CDDs), widening the forecast gap and lowering overall confidence.

Hub-Level Weather

The primary drivers of the national forecast are the Midwest and East, which show considerable model disagreement.

• Midwest (Chicago, 35% weight): The GFS is notably hotter, projecting 197.2 cumulative CDDs versus 164.5 CDDs from the ECMWF. The divergence grows significantly in the latter half of the forecast; for example, on August 11th, the GFS sees 21.1 CDDs while the ECMWF forecasts only 7.1.
• East (New York City, 30% weight): This hub shows the largest absolute disagreement. The GFS forecasts a very hot 240.6 cumulative CDDs, a full 54.2 CDDs above the ECMWF's 186.4 CDD outlook. The GFS projects a significant heatwave from August 8-11, which is much more subdued in the ECMWF solution.
• South Central (Houston, 15% weight): While both models show persistent heat, the GFS is still warmer overall, accumulating 358.0 CDDs compared to the ECMWF's 331.3 CDDs.

Demand Implications (Natural Gas)

The model disagreement translates directly to a split view on cooling-related natural gas demand (power burn).

• GFS (232.7 weighted CDDs): This outlook is strongly bullish for gas demand, implying sustained, above-normal power burn is needed to meet air conditioning load across the key population centers of the country. The significant run-over-run addition of +36.6 weighted CDDs amplifies this bullish signal.
• ECMWF (200.5 weighted CDDs): This forecast suggests a more moderate, closer-to-normal demand profile. While still indicating consistent summer cooling load, it lacks the intensity of the GFS, implying lower overall power burn. The bearish run-over-run shift of -15.5 CDDs points to a weakening demand picture compared to its prior run.

Model Agreement & Caveats

Confidence in this 15-day forecast is low due to significant model divergence and opposing run-over-run trends.

• Convergence: The official convergence_score of 0.9975 is misleadingly high. This score is based on Heating Degree Days (HDDs), which are near zero in a summer forecast. The actual agreement on Cooling Degree Days (CDDs), the relevant metric, is poor.
• Run-over-Run Shift: The models moved in opposite directions from the prior cycle, a classic sign of high atmospheric uncertainty. The GFS added significant heat while the ECMWF removed it, creating a large 52.1 weighted CDD spread between their respective 12-hour trends.
• Source: This analysis is based on GFS and ECMWF model data from Open-Meteo for a specific set of demand-weighted hubs. It may not capture all regional nuances.