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

Executive Summary

The 15-day outlook signals strong and sustained cooling demand across the U.S. Nationally, the GFS and ECMWF models are in near-perfect agreement, forecasting 211.0 and 212.6 weighted CDDs, respectively. However, this top-line agreement masks significant regional divergences, with the GFS much hotter in the South Central region while the ECMWF projects stronger heat in the Midwest and Southeast. A major run-over-run warming trend in the GFS (+27.7 weighted CDDs) adds a bullish tint to the forecast.

Hub-Level Weather

The national demand picture is primarily driven by the Midwest (Chicago, 35% weight) and the East (New York City, 30% weight). It is in these key regions, along with the South, where the models show the most conflict.

• GFS Hotter: The GFS is significantly more bullish on demand in the South Central (Houston) and East Coast hubs.

  • Houston: GFS projects 330.7 cumulative CDDs, a massive 62.9 CDDs warmer than the ECMWF's 267.8 CDDs.
  • New York City: GFS is 18.3 CDDs hotter than ECMWF (208.6 vs. 190.3), with most of the divergence occurring late in the forecast period (post July 18).

• ECMWF Hotter: The ECMWF counters with a much hotter forecast for the Midwest and Southeast.

  • Chicago: ECMWF forecasts 204.2 cumulative CDDs, which is 24.8 CDDs more intense than the GFS's 179.4 CDDs.
  • Atlanta: The largest disagreement in this direction is in the South, where ECMWF projects 298.3 CDDs, a substantial 51.9 CDDs above the GFS forecast.

Demand Implications (Natural Gas)

Both models indicate a period of above-normal power burn for natural gas is likely over the next two weeks. The key uncertainty for gas demand revolves around the geographic placement of the strongest heat.

• The GFS scenario would place greater strain on the Texas (ERCOT) power grid and drive stronger cooling load in the populous PJM and NYISO markets.
• The ECMWF scenario points to higher-than-expected demand in the Midwest (MISO/PJM) and across the Southeast.
• The most significant short-term signal is the GFS run-over-run change, which added +27.7 weighted CDDs. This substantial bullish shift suggests model guidance is trending toward a hotter overall outcome, even as the ECMWF remained relatively stable (-2.9 CDDs).

Model Agreement & Caveats

The national convergence_score of 1.0 indicates exceptionally high agreement on the total, population-weighted cooling demand. However, this top-level metric should be viewed with extreme caution.

• Caveat: The high convergence score is a result of large, offsetting regional disagreements between the models. This divergence in the placement and intensity of heat reduces overall confidence in the forecast.
• Run Stability: The GFS model showed significant volatility, trending much hotter versus its prior run. The stability of the ECMWF provides an important counterpoint. This lack of inter-model consistency warrants a cautious approach.
• Source Data: This analysis is based on deterministic GFS and ECMWF runs provided by Open-Meteo. It does not incorporate ensemble model data, which would offer a more complete view of forecast probabilities and uncertainty.