GFS vs ECMWF Demand-Hub Outlook: 2026-04-27T00:00Z

Executive Summary

The 15-day outlook shows a significant model disagreement, with the ECMWF forecasting a colder, more heating-demand-intensive period than the GFS. On a national weighted basis, the ECMWF projects ~21.5 more HDDs, driven by a much colder outlook for the East. Conversely, the GFS is substantially warmer in the South, forecasting nearly double the cooling demand (CDDs) in Texas, suggesting a much faster transition to summer power burn.

Hub-Level Weather

The primary drivers of the national forecast divergence are the high-weight eastern and southern hubs:

• East (New York City): This is the largest point of contention. ECMWF forecasts 184.3 HDDs over the 15-day period, a stark contrast to the GFS forecast of 135.8 HDDs. The difference is most pronounced in the 8-15 day range.
• South Central (Houston): The models present opposite scenarios for cooling demand. The GFS is far more bullish for power burn, calling for 175.8 CDDs, while the ECMWF is significantly milder at 89.8 CDDs.
• Midwest (Chicago): As the highest-weighted hub (0.35), this region also contributes to the colder ECMWF outlook, with the model forecasting 217.1 HDDs versus 203.6 HDDs from the GFS.

Demand Implications (Natural Gas)

This forecast presents two distinct paths for shoulder-season natural gas demand:

• ECMWF Scenario: Implies a stronger, lingering pull from residential and commercial heating demand, primarily concentrated in the high-population centers of the Midwest and Northeast. This would be supportive for late-season storage injections.
• GFS Scenario: Suggests heating demand will fade more quickly, but be partially offset by a robust start to cooling demand in the South. This would shift the demand focus from heating to power generation for air conditioning, particularly in ERCOT.

Given the time of year (late April/early May), both heating and cooling demand are significant market drivers, and the model split creates considerable uncertainty in the net demand balance. The latest model cycle saw the GFS trend warmer (-6.3 weighted HDDs), while the ECMWF was more stable (-1.4 weighted HDDs), widening the gap between the two solutions.

Model Agreement & Caveats

Confidence in this forecast should be low due to significant model disagreement.

• Convergence: The national convergence_score is 0.2356, with a weighted mean absolute HDD difference of 3.24 per day, indicating poor agreement. Model agreement worsened slightly compared to the prior run.
• Run-over-Run Trends: The GFS showed a notable warmer shift, losing 6.3 weighted HDDs from its prior run. The ECMWF was comparatively stable. This trend increased the divergence between the models.
• Source Limitations: This analysis is based on single deterministic runs from Open-Meteo. It does not account for the full range of possibilities shown in model ensembles (e.g., GEFS, EPS), which provide a better gauge of forecast uncertainty.