GFS vs ECMWF Demand-Hub Outlook: 2026-04-18T00:00Z

Executive Summary

The 15-day outlook shows a material disagreement between models, with the ECMWF forecasting significantly more late-season heating demand than the GFS. This divergence is driven almost entirely by a much colder outlook for the high-demand East Coast hubs in the ECMWF solution. Both models trended substantially colder versus their prior runs, a bullish shift for heating demand expectations heading into late April and early May.

Hub-Level Weather

The national forecast is a tale of two regions, with the primary model disagreement centered on the U.S. East.

• East (New York City): This is the main point of contention. The ECMWF is significantly colder, projecting 208.4 cumulative HDDs, while the GFS forecasts a much milder 155.9 HDDs. This ~52 HDD difference in a hub with a 30% demand weight is the largest driver of the national total variance.
• Midwest (Chicago): The most heavily weighted hub (35%) shows strong model agreement on the 15-day cumulative total, with the GFS at 187.1 HDDs and the ECMWF at 183.5 HDDs.
• South Central (Houston): Both models show emerging cooling demand with very similar totals. The GFS projects 118.6 CDDs and the ECMWF projects 116.2 CDDs.
• South (Atlanta): The GFS is notably warmer, forecasting 62.7 CDDs against just 38.0 CDDs from the ECMWF.

Demand Implications (Natural Gas)

The conflicting signals imply different risks for natural gas demand. Overall, both models trended colder, adding significant demand against the prior cycle (+14.9 weighted HDDs for GFS, +16.3 weighted HDDs for ECMWF).

• ECMWF Scenario: The colder forecast (157.3 weighted HDDs) implies a stronger-than-expected call on late-season residential and commercial heating demand, particularly in the Northeast. This would be supportive of natural gas prices by delaying the transition to the low-demand shoulder season.
• GFS Scenario: The GFS is milder on net (141.3 weighted HDDs vs 26.4 weighted CDDs). Its forecast suggests a quicker decline in heating load, offset by an earlier arrival of cooling demand in the South, which would primarily drive demand for gas-fired power generation.

Model Agreement & Caveats

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

• Convergence: The overall convergence score is 0.22, indicating a high degree of divergence between the GFS and ECMWF solutions. This low score is driven by the large forecast differences in the Eastern U.S.
• Run-over-Run Trend: The models became slightly less aligned compared to the previous cycle, as indicated by the delta in the convergence score (-0.02).
• Limitations: This analysis is based on deterministic model runs from Open-Meteo. A full ensemble analysis would be required to assess the range of potential outcomes and the true probability of either the GFS or ECMWF solution verifying.