GFS vs ECMWF Demand-Hub Outlook: 2026-04-23 00Z

Executive Summary

The GFS and ECMWF models project nearly identical national heating demand over the next 15 days (130.2 vs 129.6 weighted HDDs), but this top-level agreement masks significant regional divergence. The GFS is notably hotter in the South, forecasting higher cooling demand (+6.7 weighted CDDs), while also trending significantly colder than its prior run (+20.4 weighted HDDs). Overall forecast confidence is low due to these disagreements and model instability.

Hub-Level Weather

The national forecast is primarily driven by competing signals from the Midwest and South Central hubs.

• Midwest (Chicago, 35% weight): Models show material disagreement. The GFS is colder overall (+18.7 cumulative HDDs), but the timing differs significantly. The ECMWF projects a colder period around May 1-3, whereas the GFS shows a much colder pattern in the extended 10-15 day range.
• South Central (Houston, 15% weight): This is the key driver of the cooling demand difference. The GFS is substantially hotter, projecting 197.6 cumulative CDDs versus just 141.7 from the ECMWF (+55.9 CDDs), implying a stronger start to summer cooling load.
• East (NYC, 30% weight): Models are in better alignment, with the ECMWF projecting slightly more heating demand (+10.0 cumulative HDDs) over the period.

Demand Implications (Natural Gas)

The late-April/early-May shoulder season sees both heating and cooling demand contribute to the total gas load.

• Heating Demand: The near-identical national HDD totals suggest a similar outlook for residential/commercial heating demand from both models. However, the GFS made a significant bullish shift versus its prior cycle, adding 20.4 weighted HDDs. The ECMWF remained stable, showing almost no change (-0.7 HDDs).
• Cooling Demand (Power Burn): The GFS's warmer forecast implies a stronger call on gas-for-power generation to meet air conditioning needs, primarily in the South. The GFS projects 34.3 weighted CDDs versus 27.6 for the ECMWF. This represents a key bullish risk to power burn should the GFS solution verify.

Model Agreement & Caveats

Forecast confidence is low due to poor model agreement and a significant trend in the latest GFS run.

• Convergence: The model convergence score is low at 0.238. While the cumulative national HDD totals align, the daily path to get there differs significantly, as quantified by the weighted mean absolute daily HDD difference of 3.2. This indicates substantial disagreement on the timing and location of cold air.
• Run-over-Run Stability: The GFS's large colder shift (+20.4 weighted HDDs) from the previous cycle, contrasted with a stable ECMWF, introduces uncertainty and reduces confidence in the GFS solution.
• Source: This analysis is based on raw GFS and ECMWF model output data sourced from Open-Meteo. These are not official government forecasts and are subject to change in subsequent model runs.