GFS vs ECMWF Demand-Hub Outlook: 2026-06-29 00Z

Executive Summary

The 15-day outlook shows a significant divergence between models, with the ECMWF forecasting substantially higher national cooling demand (+41.7 weighted CDDs) than the GFS. This disagreement is driven by a much cooler GFS solution for the heavily weighted Midwest and East hubs in the Day 8-15 period. While the first week shows strong, above-normal demand, confidence beyond that is low, with the GFS trending significantly cooler (-17.9 weighted CDDs) cycle-over-cycle.

Hub-Level Weather

The national forecast is primarily driven by the two largest demand hubs, the Midwest and the East, which show major disagreement in the extended range.

• Midwest (Chicago, 35% weight): The ECMWF is significantly hotter, projecting 247.2 cumulative CDDs versus the GFS's 199.9 (+47.3 CDDs). The models align for the first 6 days before the GFS introduces a sharp cool-down starting July 5th, with mean temperatures falling into the low 70s while the ECMWF remains near 80°F.
• East (New York City, 30% weight): This hub shows the largest model disagreement. The ECMWF forecasts 319.1 cumulative CDDs, a massive 81.8 CDDs more than the GFS's 237.3. The divergence begins around July 8th, where the GFS sees a cool-down into the 70s while the ECMWF brings a second wave of intense heat with mean temperatures pushing back into the 90s.
• South Central (Houston, 15% weight): In contrast to other regions, the GFS is the warmer model here, forecasting 334.0 CDDs compared to the ECMWF's 305.5 (+28.5 CDDs).

Demand Implications (Natural Gas)

Both models indicate strong, above-normal cooling demand and associated power burn for natural gas through the first 7-8 days of the forecast. The key uncertainty for gas markets lies in the second week.

• The GFS solution points to a material drop-off in cooling demand across the key Midwest and Northeast markets after July 7th. This would significantly reduce weather-driven support for natural gas prices in the back half of the 15-day period.
• The ECMWF solution sustains strong to extreme heat in the East, implying continued robust power burn for gas generation and strong upward pressure on regional power and gas prices through the end of the forecast window.

Model Agreement & Caveats

Confidence in the 15-day forecast is high for the near-term but low for the extended range (Day 8-15).

• Convergence: The overall convergence score is high at 0.961. However, this primarily reflects strong agreement in the first week. The significant divergence in the long-range outlook, particularly in high-weight regions, suggests this headline number should be viewed with caution.
• Run-over-Run Trend: Forecast confidence has decreased since the last cycle, with the convergence score dropping by 0.026. This was driven by a large cooler trend in the GFS (-17.9 weighted CDDs), while the ECMWF was more stable (-2.1 weighted CDDs). This growing model disagreement highlights the low confidence in the extended forecast.
• Source Limitations: This analysis is based on deterministic GFS and ECMWF model runs provided by Open-Meteo. It does not include ensemble guidance, which would offer a more comprehensive view of the range of potential outcomes and overall forecast uncertainty.