GFS vs ECMWF Demand-Hub Outlook: 2026-04-22T00:00Z

Executive Summary

The 15-day outlook indicates low confidence due to significant model disagreement, particularly in the 8-15 day period. While national heating demand totals appear similar, the GFS and ECMWF models diverge sharply on a regional basis. The GFS projects a substantially hotter pattern in the South, driving higher cooling demand, while the models disagree on the timing and intensity of late-season cold in the Midwest and East. A significant warmer shift in the latest GFS run adds to forecast uncertainty.

Hub-Level Weather

The primary drivers of the national forecast show material disagreement:

• Midwest (Chicago, 35% weight): This key region shows high volatility and model divergence. The ECMWF is significantly colder from April 29th to May 1st, forecasting daily HDDs of 15.3, 21.7, and 23.0, respectively, compared to the GFS's milder 6.7, 9.6, and 13.1. The pattern then reverses, with the GFS showing a strong cold shot on May 4-5 (21.7 and 22.6 HDDs) that is much weaker in the ECMWF.
• East (New York City, 30% weight): The ECMWF is colder over the 15-day period, projecting 156.9 cumulative HDDs versus the GFS's 138.8. The main difference occurs in the medium range, such as on May 2nd where the ECMWF forecasts 16.2 HDDs against 10.6 from the GFS.
• South Central (Houston, 15% weight): The models show a major split on cooling demand. The GFS is consistently hotter, forecasting 206.2 cumulative CDDs, a stark contrast to the ECMWF's 141.2 CDDs. This divergence is most pronounced after May 1st, where the ECMWF sees a significant cool-down that the GFS misses.

Demand Implications (Natural Gas)

The forecast suggests a transitional period with competing heating and cooling demand drivers, with the net impact on natural gas consumption highly uncertain due to model differences.

• Heating Demand (Res/Comm): National weighted HDDs are nearly identical (GFS: 120.5, ECMWF: 121.7), but this masks significant regional differences. The ECMWF implies stronger heating demand in the East, while the GFS suggests late-period risk in the Midwest. The latest GFS run showed a major bearish revision, removing 37.3 weighted HDDs compared to its prior forecast, weakening the outlook for heating demand.
• Cooling Demand (Power Burn): The GFS outlook is notably more supportive for power generation demand. It forecasts 40.8 national weighted CDDs, approximately 40% higher than the ECMWF's forecast of 29.3. This difference is driven entirely by the GFS's hotter solution across the southern United States.

Model Agreement & Caveats

Forecast confidence is low, and the signal should be treated with caution.

• Convergence: The model agreement is poor, reflected in a low convergence score of 0.23. The weighted mean absolute difference in daily HDDs between the models is a significant 3.3.
• Run-over-Run Stability: The GFS model showed considerable instability, shifting 37.3 HDDs warmer and 10.1 CDDs hotter versus its previous 12z cycle. The ECMWF, by contrast, was much more stable run-over-run (+3.2 HDDs). This instability in the GFS reduces confidence in its solution.
• Data Source: This analysis is based on a limited, though demand-weighted, set of geographic hubs provided by Open-Meteo. It may not capture all regional details relevant to the national natural gas market.