GFS vs ECMWF Demand-Hub Outlook: 2026-04-28 00Z

Executive Summary

The 15-day outlook shows material disagreement between the GFS and ECMWF models, creating uncertainty for shoulder-season natural gas demand. The ECMWF is notably colder on a national weighted basis (+10.2 HDDs), driven by a significantly colder forecast for the East Coast. Conversely, the GFS is warmer in the South, projecting higher cooling demand. Confidence in the forecast is reduced as the models diverged significantly from the prior cycle, with ECMWF trending colder and GFS warmer.

Hub-Level Weather

The national forecast is a composite of conflicting regional signals, driven by the highest-weighted demand hubs:

• East (New York City, 30% weight): This is the primary source of model disagreement. The ECMWF is significantly colder, projecting 183.4 cumulative HDDs over the 15-day period, a substantial 52.5 HDDs more than the GFS forecast of 130.9.
• Midwest (Chicago, 35% weight): The models show an opposing signal here. The GFS is colder than the ECMWF, forecasting 216.0 cumulative HDDs compared to the ECMWF's 197.7 HDDs.
• South Central (Houston, 15% weight): The GFS is much warmer, driving higher cooling demand expectations. It forecasts 148.8 cumulative CDDs, which is 32.3 CDDs higher than the ECMWF's 116.5 CDD outlook.
• Northeast (Boston, 10% weight): The models are in close agreement in this region, with a cumulative HDD difference of only 4.0 (GFS: 197.9, ECMWF: 201.8).

Demand Implications (Natural Gas)

The conflicting model guidance presents a mixed outlook for natural gas consumption during this key shoulder season period.

• Heating Demand: The ECMWF solution implies a more robust and prolonged call on late-season residential/commercial heating demand, particularly in the high-consumption Eastern markets. The GFS sees a quicker drop-off in heating load in the East but more persistent cold in the Midwest. Overall, the ECMWF projects a national weighted total of 148.2 HDDs versus the GFS's 138.1 HDDs.
• Cooling Demand: The GFS outlook points to a stronger start for cooling demand, primarily for power generation in the South Central region. It projects 24.9 national weighted CDDs, while the ECMWF sees a more muted start at 19.4 CDDs.

Model Agreement & Caveats

Confidence in the 15-day forecast is moderate-to-low due to significant model divergence.

• Convergence: The convergence_score of 0.26 indicates a material level of disagreement. The weighted_mean_abs_hdd_diff_by_day is 2.79, showing notable daily variance between the models.
• Run-over-Run Shift: Forecast confidence is further undermined by a significant divergence from the previous cycle. The ECMWF trended substantially colder (+8.1 weighted HDDs), while the GFS trended warmer (-4.0 weighted HDDs). This growing disagreement suggests instability in the pattern, particularly in the Day 8-15 period.
• Source Limitations: This analysis is based on a specific set of demand-hub locations provided by Open-Meteo and does not represent a full population-weighted national average. The demand weights are illustrative.