GFS vs ECMWF Demand-Hub Outlook: 2026-07-11 00z

Executive Summary

Models present a divergent 15-day outlook, with the ECMWF forecasting a significantly stronger national cooling demand profile than the GFS. The ECMWF projects 236.5 total weighted CDDs versus the GFS's 197.8, a substantial difference of nearly 39 CDDs. This divergence is driven primarily by a much cooler GFS solution in the high-demand Midwest and Northeast hubs during the 8-15 day period, which counteracts a warmer GFS outlook in the South.

Hub-Level Weather

The primary driver of the national forecast difference is the Midwest hub (Chicago, 35% weight), where the ECMWF is drastically warmer, forecasting 263.8 cumulative CDDs versus just 179.3 from the GFS. This pattern of a much cooler GFS extends to the Northeast (Boston), where it shows only 91.5 CDDs against the ECMWF's 166.6. The GFS is so cool in this region that it generates 2.8 cumulative HDDs, a notable feature for mid-July.

Conversely, the GFS is the warmer model in southern markets. In the South Central hub (Houston), the GFS forecasts 302.0 CDDs compared to the ECMWF's 277.1. A similar dynamic is seen in the South (Atlanta), with the GFS at 237.0 CDDs versus the ECMWF's 199.8. However, these regional differences are not large enough to offset the major divergence in the more heavily-weighted northern hubs.

Demand Implications (Natural Gas)

The competing model solutions imply very different scenarios for natural gas power burn over the next two weeks. * ECMWF Scenario: The 236.5 weighted CDD forecast suggests robust and sustained cooling demand, which would support strong power generation demand for natural gas, particularly in the key Midwest and Eastern markets. * GFS Scenario: The 197.8 weighted CDD forecast points to a more moderate demand picture. It suggests a significant drop-off in cooling demand across the northern U.S. after the first week, which would pressure regional power and gas prices downward.

The run-over-run delta is notable: the GFS trended significantly warmer (+13.5 weighted CDDs) while the ECMWF was stable (-1.3 CDDs). This shift from the GFS towards the warmer ECMWF solution suggests the risk is skewed towards the higher-demand outcome.

Model Agreement & Caveats

The overall model convergence score is high at 0.9814, which improved by 0.0586 from the prior cycle. However, this high score masks significant disagreement in the latter half of the forecast period. Confidence in the near-term (1-7 days) is strong, but there is considerable uncertainty in the 8-15 day range, where the models diverge most acutely in the Midwest and Northeast. The GFS's trend toward the ECMWF solution lends some cautious credence to the warmer outlook, but the persistent gap warrants close monitoring in subsequent model runs.

Disclaimer: This analysis is based on Open-Meteo's model implementations (gfsseamless, ecmwfifs025) and a specific hub-weighting scheme. These may differ from other data providers or proprietary in-house systems.