GFS vs ECMWF Demand-Hub Outlook: 2026-04-13T00:00Z

Executive Summary

The 15-day outlook shows significant disagreement between the GFS and ECMWF models, resulting in very low forecast confidence. The ECMWF is materially colder, projecting a national heating load of 114.7 weighted HDDs, while the GFS is warmer and projects a stronger cooling load of 55.4 weighted CDDs. This divergence is most pronounced in the key Midwest and East demand hubs beyond the 7-day period.

Hub-Level Weather

The primary drivers of the national forecast are the high-weighted Midwest and East hubs, where models diverge significantly on the intensity of a late-period cooldown.

• Midwest (Chicago, 35% weight): This is a key battleground. The ECMWF is substantially colder, forecasting 143.8 cumulative HDDs versus the GFS's 112.2. The disagreement grows in the 8-15 day period; on April 23rd, for example, the GFS forecasts 3.9 CDDs while the ECMWF forecasts 6.4 HDDs.
• East (New York City, 30% weight): A similar pattern exists here, with the ECMWF forecasting nearly double the heating demand (136.8 cumulative HDDs) compared to the GFS (73.7 HDDs). The GFS suggests a transition to cooling demand late in the period, which the ECMWF does not.
• South Central (Houston, 15% weight): The models flip here, with the GFS being much hotter. It forecasts 162.7 cumulative CDDs against the ECMWF's 102.2. The ECMWF shows a brief but potent cool shot around April 20-21, generating HDDs that are absent in the GFS run.

Demand Implications (Natural Gas)

The model disagreement presents two very different scenarios for natural gas demand during this spring shoulder season.

• ECMWF Scenario: Implies a stronger-than-expected continuation of late-season heating demand, primarily from residential and commercial consumers in the Midwest and East. This outlook is more supportive for natural gas prices.
• GFS Scenario: Suggests heating demand will fade more quickly, replaced by an early arrival of notable cooling demand (power burn) in the South and, to a lesser extent, the Midwest and East. This is a more bearish outlook for demand.
• Run-over-Run Trends: Both models trended warmer on HDDs versus their prior runs (-3.88 GFS, -4.17 ECMWF). However, they diverged significantly on cooling demand: the GFS trended much hotter (+7.47 CDDs) while the ECMWF trended cooler (-5.08 CDDs), exacerbating the model differences.

Model Agreement & Caveats

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

• Convergence: The national convergence_score is 0.196, which is very low and indicates significant disagreement between the two models, particularly in the 8-15 day range.
• Divergence Drivers: The large differences in cumulative HDDs in the Midwest (delta: 31.6), East (delta: 63.1), and Northeast (delta: 44.8) are the primary sources of uncertainty.
• Source Limitations: This analysis is based on deterministic runs from Open-Meteo (gfs_seamless, ecmwf_ifs025). Ensemble model runs would be necessary to assess the full range of potential outcomes and the probability associated with each model's solution.