GFS vs ECMWF Demand-Hub Outlook: 2026-05-27 00Z

Executive Summary

The 15-day outlook shows significant model disagreement, with the GFS forecasting a much stronger combination of both heating and cooling demand than the ECMWF. The GFS is notably colder in the high-demand Midwest hub, driving a national forecast of 19.05 weighted HDDs versus the ECMWF's 10.91. Conversely, the GFS is hotter in the East and South, projecting 94.04 weighted CDDs against the ECMWF's 84.68, resulting in a low overall forecast confidence.

Hub-Level Weather

The primary drivers of the national forecast show significant divergence between models:

• Midwest (Chicago, 35% weight): This is the main point of contention. The GFS projects a significant, late-season cold spell resulting in 24.4 cumulative HDDs. The ECMWF is much warmer, forecasting only 2.2 HDDs and a much stronger 92.0 cumulative CDDs (vs. GFS's 40.1).
• East (New York City, 30% weight): Models disagree on the timing and intensity of warmth. While cumulative HDDs are similar (GFS: 8.2, ECMWF: 12.7), the GFS becomes significantly hotter in the latter half of the forecast, projecting 74.6 cumulative CDDs to the ECMWF's 32.2.
• South Central (Houston, 15% weight): Both models forecast persistent cooling demand, but the GFS is consistently hotter. It projects 281.5 cumulative CDDs, a material increase over the ECMWF's 216.3.

Demand Implications (Natural Gas)

The forecast covers a shoulder season period where weather-driven demand is typically low. However, the model disagreement presents two different scenarios:

• The GFS solution implies higher-than-expected national gas demand, driven by simultaneous heating load in the Midwest and strong cooling load across the South and East Coast.
• The ECMWF solution suggests a more moderate and purely cooling-driven demand profile, concentrated in the Midwest and South.
• Run-over-Run Shift: The GFS model saw a significant bearish shift from its prior run, losing 4.57 weighted HDDs and 3.43 weighted CDDs. This trend reduces confidence in its colder/hotter outlook and suggests momentum toward a weaker demand forecast.

Model Agreement & Caveats

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

• Convergence Score: The national convergence score is very low at 0.46, indicating significant divergence between the GFS and ECMWF solutions.
• Run Deltas: The large bearish shift in the GFS, contrasted with a relatively stable ECMWF run, highlights forecast instability. The GFS is volatile, while the ECMWF is more consistent cycle-to-cycle.
• Source Limitations: This analysis is based on raw, gridded model output from Open-Meteo for specific geographic coordinates. It does not represent official, bias-corrected station forecasts. Demand weights are illustrative for national aggregation.