GFS vs ECMWF Demand-Hub Outlook: 2026-03-29T00:00Z

Executive Summary

The 15-day outlook shows nearly identical cumulative heating demand between the GFS and ECMWF models, with both forecasting significant late-season heating load. However, this top-line agreement masks major disagreements in the timing and location of cold, particularly in the high-demand Midwest hub. Both models trended substantially warmer run-over-run (-20.9 GFS, -8.5 ECMWF weighted HDDs), presenting a less supportive demand picture than 12 hours prior.

Hub-Level Weather

The national forecast is primarily driven by heating demand in the Midwest and East, which together account for 75% of the weighted demand in this analysis.

• Midwest (Chicago, 35% weight): This is the main source of model disagreement. The GFS is materially colder overall (+17.7 cumulative HDDs vs ECMWF) but with high volatility. GFS forecasts sharp cold shots around April 2-3 (27.6 HDDs vs 15.7 for ECMWF) and April 8 (29.9 HDDs vs 8.0 for ECMWF), while the ECMWF is much colder in the April 10-11 period.
• East (New York City, 30% weight): The roles are reversed in the East, where the ECMWF is colder overall (+23.4 cumulative HDDs vs GFS). The GFS is notably warmer than the ECMWF in the final 5 days of the forecast, showing just 0.8 HDDs on April 12 compared to 15.9 for the ECMWF.
• South Central (Houston, 15% weight): Cooling demand is the primary driver. Models are in good agreement, though the GFS forecasts slightly more cooling load (+6.1 cumulative CDDs vs ECMWF), primarily in the latter part of the forecast.

Demand Implications (Natural Gas)

The forecast for late March and early April points to a period of below-normal temperatures and continued heating demand, which should support residential/commercial consumption. However, the large bearish run-over-run shift, especially in the GFS, signals a weakening demand outlook.

The significant model divergence creates high uncertainty for regional demand and pricing. The GFS scenario implies stronger heating demand in the Midwest in the 5-10 day period, while the ECMWF scenario is considerably weaker. Conversely, the ECMWF's colder outlook for the East beyond Day 10 would be more supportive for demand in that region late in the forecast. Cooling demand from the power sector is emerging in the South but is not yet a primary national driver.

Model Agreement & Caveats

Forecast confidence is low due to poor model agreement on a daily basis.

• Convergence: The weighted cumulative HDDs are nearly identical (169.6 GFS vs 169.6 ECMWF), but this is coincidental. The weighted_mean_abs_hdd_diff_by_day is a high 5.51, and the convergence_score is 0.1535 (a value > 0.1 indicates significant disagreement), highlighting the substantial differences in the day-to-day forecast.
• Instability: The GFS saw a large run-over-run change, shedding 20.9 weighted HDDs from its prior forecast. This instability reduces confidence in its current solution.
• Source Limitations: This analysis is based on single deterministic runs from Open-Meteo. It does not incorporate ensemble guidance, which would provide a fuller picture of forecast probabilities and risks. The hub-based weighting is a proxy for national demand and may not capture all regional nuances.