GFS vs ECMWF Demand-Hub Outlook: 2026-08-07 00:00 UTC

Executive Summary

The 15-day outlook shows strong summer cooling demand, though models diverge on the intensity of late-period heat. The GFS projects a significantly hotter and more demand-intensive period than the ECMWF, driven by warmer forecasts in the South. However, the GFS trended substantially cooler (-11.0 weighted CDDs) in this cycle compared to a stable ECMWF, reducing confidence in its warmer outlook.

Hub-Level Weather

The national demand picture is primarily driven by the high-weight Midwest (Chicago, 35%) and East (New York City, 30%) hubs. While the models are in close agreement for the Midwest, they show material divergence in the East and especially the South.

• South (Houston & Atlanta): This region is the primary source of model disagreement. The GFS is significantly hotter, forecasting a cumulative 355.2 CDDs in Houston and 289.4 in Atlanta, compared to the ECMWF's more modest 304.7 and 220.7, respectively.
• East (New York City): The GFS is also notably warmer here, projecting 233.0 cumulative CDDs versus 198.9 from the ECMWF. The largest daily differences appear in the 8-15 day period.
• Midwest (Chicago): The models are in tight agreement in this key hub, with both forecasting around 129-130 cumulative CDDs over the next 15 days.

Demand Implications (Natural Gas)

The forecast implies a sustained period of above-normal cooling demand, supportive for Natural Gas power burn.

• National Demand: The GFS's hotter forecast projects 209.6 demand-weighted CDDs, implying a more bullish scenario for NG futures than the ECMWF's 190.4 CDDs.
• Run-over-Run Shift: The GFS model saw a significant bearish shift, losing 11.0 weighted CDDs from its prior 06z run. In contrast, the ECMWF was very stable, shedding just 0.7 CDDs. This major GFS revision toward a cooler solution suggests its remaining heat forecast may be less reliable.

Model Agreement & Caveats

Overall model agreement remains high, but recent trends warrant caution.

• Convergence: The model convergence score is a high 0.9827, though this is a slight decrease from the prior cycle. Agreement is strongest in the first 7-10 days, with the most significant divergence occurring in the extended range.
• Caveats: The primary caveat is the GFS model's instability. Its large cooler revision in this cycle, while the ECMWF held steady, suggests the operational GFS may be converging towards the ECMWF's less-hot solution. Therefore, the ECMWF's more moderate demand forecast should be weighted more heavily despite the high-level convergence score.
• Source: This analysis is based on GFS & ECMWF model data from Open-Meteo, which provides deterministic forecasts and does not include ensemble or probabilistic data that could offer a wider range of potential outcomes.