GFS vs ECMWF Demand-Hub Outlook: 2026-04-02T00:00Z

Executive Summary

The 15-day outlook shows the GFS forecasting more heating demand than the ECMWF (173.5 vs 161.0 weighted HDDs), a difference driven entirely by a significantly colder GFS outlook in the high-demand Midwest hub. However, confidence in the GFS solution is low, as the model trended substantially warmer in this cycle (-24.6 weighted HDDs), while the ECMWF remained stable. Both models show emerging, and well-agreed-upon, cooling demand in the southern U.S.

Hub-Level Weather

The national forecast masks significant regional disagreements between the models, particularly in the Day 8-15 period.

• Midwest (Chicago, 35% weight): This is the primary point of contention. The GFS is materially colder, projecting 255.9 total HDDs versus the ECMWF's 192.4 HDDs. The divergence is most pronounced after April 9th, where the GFS brings in a late-season cold shot that the ECMWF does not see.
• East (New York City, 30% weight): The models show the opposite pattern here, with the ECMWF forecasting more heating demand (198.1 HDDs) compared to the GFS (171.4 HDDs).
• South (Houston & Atlanta, 25% combined weight): Model agreement is high in the South. Both forecasts show consistent, spring-like warmth driving cooling demand. Houston is projected to see ~98-103 CDDs, with minimal heating load.

Demand Implications (Natural Gas)

The forecast points to typical shoulder season conditions, with weather-driven demand transitioning from heating to cooling.

• Heating Demand: The overall HDD forecast is moderate. The GFS's colder Midwest outlook implies a stronger call on natural gas for residential/commercial heating demand relative to the ECMWF. The ECMWF's warmer scenario would result in looser balances.
• Cooling Demand: Both models forecast a similar level of early-season cooling demand (GFS: 19.5 weighted CDDs, ECMWF: 21.5 weighted CDDs), concentrated in the South Central and Southeast regions. This will generate some initial power sector gas demand for cooling.

Model Agreement & Caveats

Overall model agreement has weakened since the last cycle, warranting caution.

• Convergence: The convergence score of 0.167 indicates moderate disagreement, primarily driven by the large HDD differential in Chicago (mean_abs_hdd_diff_by_day: 7.75). The score increased by 0.0214 from the prior run, signaling that the models are diverging.
• Run-over-Run Deltas: The most significant signal is the change from the prior 00Z cycle. The GFS lost a substantial 24.6 weighted HDDs, indicating its solution is unstable. In contrast, the ECMWF was very stable, adding only 1.9 weighted HDDs. This instability reduces confidence in the GFS's colder forecast.
• Source Data: This analysis is based on raw, non-bias-corrected model output from Open-Meteo. Forecasts, especially beyond 7-10 days, are subject to significant revisions.