GFS vs ECMWF Demand-Hub Outlook: 2026-09-21 00z

Executive Summary

Models show significant disagreement over the 15-day forecast, resulting in a low confidence signal for Natural Gas demand. The GFS projects a much warmer and stronger cooling demand scenario (83.8 weighted CDDs) compared to the more seasonal and colder ECMWF (37.9 weighted HDDs, 46.3 weighted CDDs). This divergence is driven by a major bullish (warmer) shift in the GFS model run-over-run, while the ECMWF remained stable.

Hub-Level Weather

The national demand picture is driven by stark differences in the two highest-weighted regions:

• Midwest (Chicago, 35% weight): The models diverge significantly in the second week. The GFS is notably warmer, projecting only 40.1 cumulative HDDs and a late surge of cooling demand (28.6 CDDs). The ECMWF is colder and more seasonal, forecasting 49.2 HDDs and negligible cooling demand (2.4 CDDs).
• East (New York City, 30% weight): The disagreement is even more pronounced here. The GFS forecasts a very warm period with only 17.3 HDDs and a substantial 45.5 CDDs. In contrast, the ECMWF sees a much colder pattern developing, calling for 46.4 HDDs and only 11.3 CDDs.
• South Central (Houston, 15% weight): The GFS maintains strong, late-season heat, forecasting 311.2 CDDs. The ECMWF is significantly cooler, particularly after Day 8, and projects only 238.0 CDDs for the period.

Demand Implications (Natural Gas)

The conflicting outlooks present two very different scenarios for NG futures.

• GFS Scenario (More Bullish): The GFS outlook, with its combination of low heating demand (26.5 weighted HDDs) and strong cooling demand (83.8 weighted CDDs), would be supportive of prices. The high CDD count implies robust power burn to meet air conditioning load, particularly in the South and East. This run represents a significant bullish change from its prior forecast (-25.8 HDDs, +27.8 CDDs).

• ECMWF Scenario (More Bearish): The ECMWF shows a more bearish picture for demand. Its forecast for weaker cooling (46.3 weighted CDDs) and only modest, early-season heating (37.9 weighted HDDs) points to a period of lower weather-driven demand. The model's stability run-over-run (-1.3 HDDs, -9.4 CDDs) lends credibility to this more moderate outlook.

Model Agreement & Caveats

Confidence in this forecast is low due to poor model agreement.

• Convergence Score: The national convergence score is 0.34, indicating significant disagreement between the GFS and ECMWF solutions, particularly in the 8-15 day range.
• Model Volatility: The GFS experienced a major shift warmer versus its previous run. Such large changes often suggest model instability and increase the risk of a reversal in subsequent cycles. The ECMWF's relative consistency is a point in its favor.
• Source Limitations: This analysis is based on a snapshot from Open-Meteo's processing of the GFS and ECMWF 00z model runs. It provides a demand-weighted view but does not encompass all available weather model guidance.