GFS vs ECMWF Demand-Hub Outlook: 2026-08-02 00Z

Executive Summary

The 15-day outlook shows a material model disagreement, with the GFS projecting a hotter national forecast than the ECMWF (+13.75 weighted CDDs). This divergence is driven almost entirely by the GFS showing a significantly hotter pattern across the East (NYC, Atlanta), while the ECMWF is warmer in the Midwest. Run-over-run changes show the GFS trending significantly cooler (-6.5 CDDs) while the ECMWF trended slightly warmer (+1.4 CDDs), reducing confidence in the GFS's hotter solution.

Hub-Level Weather

The primary drivers of the national demand forecast, the Midwest and East, show significant model disagreement.

• East (New York City & Atlanta): This is the epicenter of the model divergence. The GFS is substantially hotter, projecting +54.0 CDDs more than ECMWF in NYC and +47.9 CDDs more in Atlanta over the 15-day period. The GFS shows a period of intense heat from approximately August 6th to 10th that is absent in the ECMWF.
• Midwest (Chicago): In contrast to the East, the ECMWF is the warmer model in this key hub, forecasting +15.0 CDDs more than the GFS. The primary separation occurs later in the forecast, particularly from August 11th-12th.
• South Central (Houston): The models are in close agreement, with both showing sustained, strong heat. The GFS projects 337.0 CDDs and the ECMWF projects 333.2 CDDs, a negligible difference for this high-demand region.

Demand Implications (Natural Gas)

The forecast universally points to strong cooling demand, as expected for early August. However, the regional differences carry significant implications for natural gas power burn.

• The GFS solution implies robust, likely above-normal, power burn concentrated in the high-population centers of the East Coast.
• The ECMWF solution points to a more moderate demand profile in the East, offset by stronger cooling demand in the Midwest. Overall, the ECMWF implies a lower national power burn total than the GFS.
• The significant run-over-run cooler trend in the GFS suggests its hotter Eastern solution may be unstable and could continue to correct toward the ECMWF's more moderate outlook.

Model Agreement & Caveats

• Confidence: Confidence in the forecast is low due to the stark regional disagreements and opposing run-over-run model trends.
• Convergence: While the convergence_score is 1.0, this headline number masks the material hub-level disagreements noted above. The GFS's total weighted forecast of 221.98 CDDs is 7% higher than the ECMWF's 208.23 CDDs.
• Run-over-Run Shift: The GFS trended 6.5 weighted CDDs cooler versus its prior cycle, while the ECMWF added 1.4 CDDs. This divergence between consecutive runs is a key indicator of forecast uncertainty.
• Source Note: This analysis is based on deterministic model runs sourced via the Open-Meteo API. For a complete risk assessment, ensemble guidance should be consulted to understand the full range of potential outcomes.