GFS vs ECMWF Demand-Hub Outlook: 2026-07-21T00:00Z

Executive Summary

The 15-day outlook shows sustained cooling demand, with the GFS model forecasting a moderately higher national load than the ECMWF. The GFS projects 195.0 total population-weighted CDDs versus 186.1 on the ECMWF. Despite large regional disagreements, overall model agreement is exceptionally high (convergence score: 0.997), lending strong confidence to the general theme of summery temperatures. Both models trended warmer compared to their prior cycles.

Hub-Level Weather

The national picture is driven by significant, offsetting disagreements in the two largest demand hubs:

• Midwest (Chicago, 35% weight): The ECMWF is substantially hotter, forecasting 169.7 cumulative CDDs compared to the GFS's 143.6 CDDs. The divergence is most pronounced in the Day 5-11 period (July 25-31).
• East (New York City, 30% weight): The GFS is the hotter model in this key region, projecting 185.1 cumulative CDDs versus the ECMWF's 147.5. The main difference emerges in the latter third of the forecast (post-August 1st).
• South / South Central (Houston & Atlanta, 25% combined weight): The GFS is consistently hotter across the South, contributing to its higher national total. It forecasts a combined 636.8 CDDs for these hubs, while the ECMWF forecasts 570.4 CDDs.

Demand Implications (Natural Gas)

The forecast implies a strong and sustained call on natural gas for power generation to meet air conditioning needs throughout the 15-day period.

• The GFS solution (+8.9 weighted CDDs vs ECMWF) suggests a moderately stronger demand profile, particularly centered in the East and South.
• The ECMWF scenario points to a greater demand risk concentrated in the Midwest.
• Compared to the previous cycle, both models added demand (+6.2 weighted CDDs for GFS, +5.7 for ECMWF), signaling a strengthening forecast for power burn.

Model Agreement & Caveats

Confidence in the overall theme of above-normal cooling demand is very high, supported by a convergence_score of 0.997 (where 1.0 is perfect agreement).

• Caveat: The high top-line agreement masks the significant regional model divergence noted above. The relatively small national difference is a product of large, offsetting regional forecasts. This lowers confidence in either specific regional outcome and warrants close monitoring in subsequent model runs.
• Run-over-Run Trend: The consistent warmer trend across both models in this cycle reinforces the high-demand outlook.
• Limitations: This analysis is based on deterministic GFS and ECMWF runs from Open-Meteo. It does not incorporate probabilistic ensemble data, which provides a range of potential outcomes, nor does it include other global models. Hub locations are proxies for broader demand regions.