GFS vs ECMWF Demand-Hub Outlook: 2026-07-15 00Z

Executive Summary

The 15-day outlook shows broad agreement on the national cooling demand total, with the ECMWF forecasting a slightly stronger 207.9 weighted CDDs versus the GFS at 202.3. However, this masks significant regional disagreements; the ECMWF is substantially hotter in the high-demand Midwest, while the GFS projects much more intense heat across the South and South Central hubs. Both models have trended cooler since their prior runs, slightly reducing the overall demand forecast.

Hub-Level Weather

The national forecast is primarily driven by two key regions with opposing model signals:

• Midwest (Chicago, 35% weight): This is the main point of contention. The ECMWF is significantly hotter, forecasting 209.3 CDDs compared to just 169.5 CDDs from the GFS over the 15-day period.
• South / South Central (Houston & Atlanta, 25% combined weight): The GFS is materially hotter in the South. In Houston, GFS projects 325.1 CDDs vs. the ECMWF's 278.7 CDDs. In Atlanta, the divergence is even more stark, with GFS at 242.4 CDDs versus the ECMWF's 189.8 CDDs.
• East (New York City, 30% weight): Models are in close alignment for this key hub, with the GFS at 193.9 CDDs and the ECMWF at 197.2 CDDs.

Demand Implications (Natural Gas)

The forecast points to a period of strong, seasonal power burn for cooling. The key uncertainty for national gas demand is which regional solution verifies.

• If the ECMWF's hotter Midwest forecast is correct, gas demand for power generation could be stronger than the GFS implies, particularly in a region with significant residential and commercial load.
• Conversely, if the GFS's intense heat across Texas and the Southeast materializes, regional power burn will be extremely strong, potentially stressing local grids and driving gas demand higher there.
• Compared to the previous model cycle, the outlook has weakened slightly. The GFS lost 7.4 weighted CDDs, and the ECMWF lost 4.4 weighted CDDs, suggesting a moderation in previously forecast heat.

Model Agreement & Caveats

The national-level convergence_score is a perfect 1.0, reflecting the very close weighted cumulative totals. However, this high-level score is misleading and should be treated with caution.

• The underlying regional disagreements between the Midwest and the South are significant and represent the primary forecast risk. Confidence in the distribution of national demand is low.
• This analysis relies on deterministic model runs. Ensemble guidance would be required to assess the probability of each regional outcome and the full range of possibilities.
• Data is sourced from Open-Meteo and is based on a specific set of demand-hub proxies; it may not capture all regional load variations.