GFS vs ECMWF Demand-Hub Outlook: 2026-07-10 00:00Z

Executive Summary

The 15-day outlook points to sustained cooling demand, with the ECMWF model forecasting a materially stronger national load profile than the GFS. The ECMWF projects 233.4 demand-weighted Cooling Degree Days (CDDs), compared to 202.5 CDDs from the GFS. This divergence is primarily driven by a significantly hotter ECMWF forecast in the high-demand Midwest and East hubs, which is only partially offset by a hotter GFS solution in the South. Both models have trended significantly hotter compared to their prior runs, adding a bullish tint to the demand outlook.

Hub-Level Weather

The largest demand-weighted hubs are the primary drivers of model disagreement:

• Midwest (Chicago, 35% weight): This is the single largest point of divergence. The ECMWF is substantially hotter, forecasting 239.8 cumulative CDDs versus the GFS's 175.8 (+64 CDDs). The disagreement grows significantly in the 8-15 day period.
• East (New York City, 30% weight): The ECMWF is also warmer here, projecting 223.3 CDDs against the GFS's 196.5 (+26.8 CDDs), with most of the separation occurring late in the forecast period. This trend is amplified in Boston (10% weight), where the ECMWF is +56.5 CDDs warmer and avoids a late-period cool shot forecasted by the GFS that generates 5.1 HDDs.
• South (Atlanta, 10% weight): In contrast to other regions, the GFS is the hot outlier here, forecasting 279.3 CDDs against the ECMWF's 218.6 (+60.7 CDDs).
• South Central (Houston, 15% weight): Both models are in close agreement, showing persistent strong cooling demand with cumulative CDDs of 292.3 (GFS) and 298.4 (ECMWF).

Demand Implications (Natural Gas)

The forecast implies a robust period of power burn for natural gas, driven by air conditioning load.

• ECMWF Scenario: The European model's solution would generate stronger, more widespread, and sustained natural gas demand for power generation, especially across the densely populated Midwest and Northeast markets.
• GFS Scenario: The American model suggests a slightly weaker national demand profile, with periods of cooler relief in the Northeast that could temper regional power burn if verified. Its offsetting heat is focused in the less demand-elastic Southeast.
• Run-over-Run Trend: Both models added significant demand compared to their prior 6-hour runs. The GFS added +12.5 weighted CDDs and the ECMWF added a substantial +34.4 weighted CDDs, signaling a strengthening conviction in upcoming heat.

Model Agreement & Caveats

Confidence in the overall pattern of summer heat is high, but lower regarding the regional intensity and distribution.

• Convergence: The national demand-weighted convergence_score is high at 0.967. However, this top-line number masks the significant regional disagreements outlined above. While the total national CDD forecast is somewhat close, the models achieve it through very different weather patterns (ECMWF hot North vs. GFS hot South).
• Caveats: Forecast uncertainty increases materially beyond day 7, where the model solutions diverge most. This analysis is based on a limited set of demand hubs provided by Open-Meteo and does not represent a full, population-weighted national aggregate.