GFS vs ECMWF Demand-Hub Outlook: 2026-04-05 00z

Executive Summary

The 15-day outlook shows significant disagreement between models, with the ECMWF forecasting a materially colder and more demand-heavy period than the GFS. The ECMWF projects 211.5 demand-weighted HDDs, a substantial 33.8 HDDs more than the GFS's 177.7. This divergence is driven primarily by a much colder forecast for the East in the 8-15 day period. Confidence in either forecast is low due to the poor model agreement, though the GFS trended colder run-over-run, adding +6.6 weighted HDDs.

Hub-Level Weather

The national divergence is almost entirely attributable to the major population centers in the Midwest and East, which carry the highest demand weights.

• East (New York City, 30% weight): This is the primary source of disagreement. The ECMWF is dramatically colder, forecasting 244.0 cumulative HDDs versus just 169.7 HDDs from the GFS. The difference of over 74 HDDs is concentrated in the latter half of the forecast; for example, on April 15th, the GFS sees only 1.8 HDDs while the ECMWF forecasts a much colder 22.1 HDDs.
• Midwest (Chicago, 35% weight): A similar, though less extreme, pattern is present here. The ECMWF projects 289.5 HDDs compared to the GFS's 258.1 HDDs. The ~31 HDD gap also emerges in the 8-15 day period.
• South Central (Houston, 15% weight): In contrast to heating demand in the north, the GFS is warmer in the south, forecasting the first notable cooling demand of the season with 82.8 cumulative CDDs, compared to a more modest 55.5 CDDs from the ECMWF.

Demand Implications (Natural Gas)

The model disagreement presents two starkly different scenarios for natural gas demand.

• ECMWF Scenario: The colder outlook implies sustained, above-normal residential/commercial heating demand deep into April, particularly for the high-consumption East and Midwest markets. This would be bullish for natural gas prices, delaying the end of the heating season and slowing the start of inventory injections.
• GFS Scenario: The GFS depicts a more typical shoulder-season transition, with heating demand fading significantly after the first week and being partially offset by early-season cooling demand (power burn) in the South. While the GFS is the warmer model, its significant colder trend in this cycle (+6.6 weighted HDDs) warrants attention as it may be converging toward the ECMWF's solution.

Model Agreement & Caveats

Confidence in this 15-day forecast is low.

• Convergence: The model convergence score is 0.1848, indicating poor agreement and high forecast uncertainty. The weighted mean absolute HDD difference per day is a high 4.4 HDDs, confirming the significant day-to-day spread between the models.
• Caveats: The most significant divergence occurs in the 8-15 day range, which is inherently less reliable. Traders should treat this portion of the forecast with extreme caution until subsequent model runs provide a clearer, more unified signal.
• Source Limitations: This analysis is based on deterministic GFS and ECMWF runs from Open-Meteo. It does not incorporate ensemble data, which would provide a better sense of the full range of potential outcomes. The hub-weighting system is representative but is not a complete model of all U.S. natural gas demand.