GFS vs ECMWF Demand-Hub Outlook: 2026-04-08T00:00Z

Executive Summary

The 15-day outlook shows a significant divergence between models, with the GFS forecasting a colder, more heating-demand-intensive period for the northern U.S. compared to a notably warmer ECMWF solution. The ECMWF made a substantial shift warmer run-over-run, shedding 16.7 HDDs and adding 7.8 CDDs, suggesting the overall pattern is trending less supportive for heating demand. Confidence in the forecast is moderate due to the model disagreement, with the primary split occurring in the key Midwest and East consumption hubs.

Hub-Level Weather

The main drivers of the national forecast are the high-weighted hubs in the Midwest and East, where the models show their largest disagreements on heating demand.

• Midwest (Chicago, 35% weight): The GFS is materially colder, forecasting 186.3 cumulative HDDs versus 162.6 HDDs from the ECMWF. The ECMWF also introduces significant late-period cooling demand (17.2 CDDs) that is almost entirely absent in the GFS (0.6 CDDs).
• East (New York City, 30% weight): This hub shows the most substantial HDD disagreement. The GFS forecasts 183.4 HDDs, a full 42.8 HDDs more than the ECMWF's 140.6 HDDs. The ECMWF is consistently warmer through the medium and long range.
• South Central (Houston, 15% weight): This region is purely a cooling story. The GFS is the hotter of the two models here, projecting 160.6 cumulative CDDs compared to the ECMWF's 131.9 CDDs.

Demand Implications (Natural Gas)

The competing model outlooks imply different trajectories for shoulder season natural gas demand.

• Total Demand-Weighted Load: Nationally, the GFS forecasts 146.9 weighted HDDs, while the ECMWF is significantly lower at 122.6 weighted HDDs. Cooling demand is nearly identical between the models (35.8 GFS CDD vs 36.5 ECMWF CDD).
• Heating Demand (Res/Com): The GFS solution would prolong notable residential and commercial heating demand, particularly in the high-consumption Northeast and Midwest markets.
• Cooling Demand (Power): The ECMWF's warmer outlook erodes heating demand more quickly and hints at an earlier start to cooling load in northern markets. The hotter GFS in the South implies stronger early-season power burn for gas generation in Texas.
• Run-Over-Run Shift: Both models trended warmer versus the prior cycle, with the ECMWF's large -16.7 HDD adjustment being the most significant change. This trend lends weight to the warmer scenario being more probable.

Model Agreement & Caveats

Confidence in the 15-day forecast is moderate due to material model disagreement, particularly in the Day 8-15 range.

• Convergence: The convergence score of 0.24 and a weighted mean absolute HDD difference of 3.1 per day indicate a notable lack of consensus. The models have diverged further since the last cycle, as shown by the delta convergence score of +0.04.
• Caveats: This analysis is based on a limited number of demand hubs and may not perfectly represent a full CONUS population-weighted forecast. Forecast skill diminishes significantly beyond day 7. The data is provided by Open-Meteo's free tier API, which has limitations on resolution and update frequency compared to commercial providers.