GFS vs ECMWF Demand-Hub Outlook: 2026-07-13T00:00Z

Executive Summary

The 15-day outlook points to strong summer cooling demand, with the ECMWF forecasting a slightly higher national load (237.0 weighted CDDs) than the GFS (224.7 weighted CDDs). Models show significant regional disagreement; the ECMWF is substantially hotter in the high-demand Midwest and East for the first week, while the GFS projects more intense and sustained heat across the South. Run-over-run model trends diverged, with the GFS adding 13.1 CDDs while the ECMWF shed 8.9 CDDs, indicating some forecast uncertainty.

Hub-Level Weather

The national demand-weighted totals mask significant differences at the regional hub level:

• Midwest (Chicago, 35% weight): This is the largest point of disagreement. The ECMWF is significantly hotter, forecasting 261.0 cumulative CDDs versus the GFS's 218.1. The difference is concentrated in the first week, where for example on July 14th, the ECMWF forecasts a mean temperature of 90.0°F while the GFS sees only 81.6°F.
• East (NYC, 30% weight): The ECMWF is also hotter here, projecting 233.8 CDDs to the GFS's 216.5. This heat is front-loaded in the Day 2-9 period before the GFS becomes the warmer model at the end of the forecast.
• South (Atlanta, 10% weight): The models are inverted in the South. The GFS is substantially hotter, forecasting 267.6 CDDs against the ECMWF's 183.6. The GFS projects a multi-day stretch of 90°F+ mean temperatures (July 20-21) where the ECMWF remains in the upper 70s.
• South Central (Houston, 15% weight): The GFS is also warmer in this region, totaling 290.9 CDDs versus 271.7 for the ECMWF, with most of the divergence occurring in the Day 5-12 period.

Demand Implications (Natural Gas)

Both models indicate a period of robust, above-normal cooling demand, which implies strong natural gas consumption for power generation (power burn).

• The ECMWF solution suggests a more intense, front-loaded demand event centered on the key population hubs of the Midwest and Northeast.
• The GFS solution, while still showing strong national demand, shifts the focus of the most anomalous heat and associated power burn to the South and South Central regions, particularly in the 6-10 day period.
• The GFS trended significantly hotter (+13.1 weighted CDDs) compared to the prior cycle, a bullish signal. Conversely, the ECMWF's cooler trend (-8.9 CDDs) tempers this signal and suggests the overall pattern remains volatile.

Model Agreement & Caveats

The forecast has a high-level convergence_score of 1.0, reflecting that the total 15-day national demand-weighted CDDs are within ~5% of each other.

• Caveat: This national agreement conceals major regional disagreements on the placement and timing of the strongest heat. This divergence reduces confidence in predicting which specific regions will experience peak power burn.
• Caveat: The opposing run-over-run trends (GFS hotter, ECMWF cooler) further highlight uncertainty and suggest the atmospheric pattern is not yet locked in, particularly in the latter half of the forecast.
• Source Note: This analysis is based on publicly available GFS and ECMWF data from Open-Meteo. This data may differ from proprietary, value-added weather services tailored specifically for the energy industry.