GFS vs ECMWF Demand-Hub Outlook: 2026-05-01T00:00Z

Executive Summary

The 15-day outlook shows a material disagreement between models, with the ECMWF forecasting significantly more heating demand than the GFS, while the GFS projects higher cooling demand. This divergence is primarily driven by the ECMWF being substantially colder in the heavily-weighted Midwest (Chicago hub), and the GFS being warmer in the South Central (Houston hub). The latest GFS run trended significantly colder, adding demand and narrowing the gap with the ECMWF, but overall model agreement remains low.

Hub-Level Weather

The key drivers of the national demand forecast show significant model divergence:

• Midwest (Chicago, 35% weight): This is the largest point of disagreement. The ECMWF is markedly colder, projecting 255.1 HDDs over the 15-day period, compared to just 208.6 HDDs from the GFS. This ~46 HDD difference in the most influential hub is the primary driver of the national heating demand discrepancy.
• East (New York City, 30% weight): A similar, though less pronounced, pattern exists here. The ECMWF forecasts 162.1 HDDs versus 132.5 HDDs from the GFS, a difference of nearly 30 HDDs.
• South Central (Houston, 15% weight): The models diverge on cooling demand in the south. The GFS is much warmer, forecasting 135.0 CDDs, while the ECMWF projects a more modest 78.1 CDDs.

Demand Implications (Natural Gas)

The conflicting model outlooks present two distinct scenarios for natural gas demand:

• Heating Demand: The ECMWF's colder forecast implies stronger-than-expected late-season heating demand, with 164.1 weighted HDDs nationally. The GFS is less supportive for heating demand at 134.7 weighted HDDs.

  • Run-over-Run Delta: The GFS made a significant shift colder in this cycle, adding +14.3 weighted HDDs compared to its prior run. The ECMWF remained stable (+0.5 weighted HDDs). This trend suggests the GFS is moving toward the ECMWF's colder solution, but a large gap persists.

• Cooling Demand: The GFS indicates an earlier start to significant cooling load, projecting 24.3 weighted CDDs, driven by warmth in the South. The ECMWF sees a more muted start to the cooling season with only 15.3 weighted CDDs.

  • Run-over-Run Delta: The GFS trended notably less warm, shedding -9.7 weighted CDDs from its prior forecast.

Model Agreement & Caveats

Confidence in this forecast is low due to significant model disagreement.

• Convergence Score: The current convergence score is 0.255, which indicates a material lack of agreement between the two models. This score worsened slightly from the prior run (delta: +0.059), signaling increasing uncertainty.
• Divergence Drivers: The low confidence is a direct result of the conflicting temperature forecasts in the Midwest and South Central hubs. Until the models come into better alignment for these key demand centers, particularly in the 6-15 day range, the overall demand signal should be treated with caution.
• Source: This analysis is based on publicly available GFS and ECMWF model data from Open-Meteo. It does not incorporate ensemble means or proprietary model blends, which may offer a more nuanced view.