GFS vs ECMWF Demand-Hub Outlook: 2026-07-01T00:00Z

Executive Summary

The 15-day outlook shows nearly identical national cooling demand totals between the GFS (240.3 weighted CDDs) and ECMWF (238.2 weighted CDDs). However, this top-line agreement masks significant and offsetting regional disagreements, particularly in the 8-15 day period. The GFS projects intense heat across the South, while the ECMWF is substantially hotter in the high-demand Midwest. The GFS model also trended significantly cooler run-over-run, reducing confidence in its latest solution.

Hub-Level Weather

The national demand picture is primarily driven by the Midwest (Chicago, 35% weight) and the East (NYC, 30% weight). It is in these key regions where the models diverge most critically.

• Midwest (Chicago): The ECMWF is significantly hotter, forecasting 230.3 cumulative CDDs versus the GFS's 191.1 CDDs. This +39.2 CDD difference is concentrated in the latter half of the forecast (post July 11th).
• South (Atlanta & Houston): The GFS is dramatically hotter. In Atlanta, GFS is +101.4 CDDs above the ECMWF (324.5 vs 223.1). In Houston, the GFS is +38.4 CDDs hotter (338.9 vs 300.5).
• East (New York City): The models are in close agreement, with the GFS showing 250.9 CDDs and the ECMWF 245.1 CDDs over the 15-day period.

Demand Implications (Natural Gas)

The overall forecast points to a period of strong summer cooling demand, driving natural gas consumption for power generation. The key uncertainty for national load is which regional model solution proves more accurate.

• The offsetting nature of the forecasts (ECMWF's hot Midwest vs. GFS's hot South) creates a volatile outlook. A shift toward either model's solution in subsequent runs would have a material impact on the national demand forecast.
• Given the significant cooling trend in the latest GFS run (-11.0 weighted CDDs) versus a stable ECMWF run (-0.7 weighted CDDs), the market may lean more heavily on the ECMWF's hotter Midwest / cooler South scenario.

Model Agreement & Caveats

Confidence in the national demand total is superficially high, but confidence in the regional distribution of that demand is very low.

• Convergence: The national convergence_score is 1.0, indicating near-perfect agreement on the weighted national total. This metric should be viewed with extreme caution as it completely masks the large, offsetting regional disagreements noted above.
• Run-over-Run Trends: The GFS shifted materially cooler by -11.0 weighted CDDs from its prior cycle. The ECMWF remained very stable, shifting by only -0.7 weighted CDDs. This lack of consistency from the GFS reduces its forecast credibility for this cycle.
• Source Limitations: This analysis is based on raw GFS and ECMWF model output from Open-Meteo. Forecasts, particularly beyond Day 7, are subject to significant change in subsequent model runs.