GFS vs ECMWF Demand-Hub Outlook: 2026-04-29T00:00Z

Executive Summary

The 15-day outlook shows a significant divergence between models, with the ECMWF forecasting a colder, more supportive scenario for natural gas heating demand, while the GFS suggests a much warmer period with an earlier onset of cooling demand. A major warmer trend in the latest GFS run (-48.0 demand-weighted HDDs) adds uncertainty, contrasting with a stable ECMWF. Overall, the ECMWF projects 130.23 weighted HDDs versus the GFS's 109.68, a material difference driven by the Eastern U.S.

Hub-Level Weather

The primary drivers of the national forecast divergence are the high-weight demand hubs in the East and South.

• East (New York City): This hub shows the most significant disagreement on heating demand. The ECMWF is substantially colder, forecasting 140.20 cumulative HDDs over the 15-day period, while the GFS forecasts only 93.63 HDDs. This difference is concentrated in the 6-15 day range.
• Midwest (Chicago): While closer on total heating demand (186.4 HDDs on ECMWF vs. 174.9 on GFS), the models diverge on the timing of a late-period warmup. The GFS introduces significant cooling demand (22.6 CDDs) in the final three days, a signal not present in the ECMWF (12.0 CDDs).
• South Central (Houston): As the primary cooling hub, the GFS is significantly hotter, projecting 145.9 cumulative CDDs compared to just 79.7 on the ECMWF. This points to a much stronger call on gas-for-power generation in the GFS outlook.

Demand Implications (Natural Gas)

This forecast occurs during the spring shoulder season, where demand is sensitive to both late-season heating and early-season cooling.

• Heating Demand: The ECMWF forecast implies a continuation of meaningful residential/commercial heating demand, particularly in the East. Its 15-day total of 130.2 weighted HDDs is supportive for this time of year.
• Cooling Demand: The GFS outlook is more bearish for heating demand but signals an early start to summer power burn. It forecasts nearly double the national weighted cooling demand of the ECMWF (35.4 GFS CDDs vs. 18.5 ECMWF CDDs), led by a hot pattern in the South.
• Run-over-Run Shift: The GFS trended sharply warmer versus its prior run, shedding -48.0 weighted HDDs. This is a significant bearish shift. In contrast, the ECMWF remained stable (+0.5 weighted HDDs), lending more credence to its colder solution for now.

Model Agreement & Caveats

Confidence in the 15-day outlook is low due to material model disagreement.

• Convergence: The national convergence score of 0.2688 indicates notable disagreement, which has slightly increased since the prior model cycle. The demand-weighted average absolute difference between the models is 2.72 HDDs per day.
• Caveats: The largest discrepancies appear in the 8-15 day period, where forecast skill is inherently lower. The significant warmer trend in the GFS is a key watch item; if the ECMWF trends in a similar direction in subsequent runs, it would confirm a less supportive outlook. This analysis is based on publicly available Open-Meteo model data and may differ from specialized, proprietary weather services.