GFS vs ECMWF Demand-Hub Outlook: 2026-04-26 00Z

Executive Summary

The 15-day outlook indicates a classic shoulder season pattern, with lingering heating demand across the northern U.S. and building cooling demand in the South. While the GFS and ECMWF models are closely aligned on a total national weighted basis (ECMWF is only 5.3 weighted HDDs colder), this masks significant regional disagreements and forecast instability. The latest model cycle saw the GFS trend significantly colder (+12.1 WHDDs) while the ECMWF trended warmer (-8.2 WHDDs), reducing overall forecast confidence despite their similar endpoints.

Hub-Level Weather

The national picture is primarily driven by opposing forecasts for the two largest demand hubs, which comprise 65% of the total demand weight.

• Midwest (Chicago, 35% weight): The GFS is materially colder, forecasting 200.6 HDDs versus 183.3 HDDs on the ECMWF (+17.3 HDDs). This divergence is concentrated in the Day 10-13 period (May 5-8).
• East (New York City, 30% weight): The ECMWF is significantly colder here, projecting 171.7 HDDs against the GFS's 143.1 HDDs (+28.6 HDDs). The largest split occurs in the Day 7-10 range (May 2-6), where the GFS shows a much warmer pattern.
• South Central (Houston, 15% weight): Both models show consistent cooling demand. The GFS is hotter, with 167.0 CDDs compared to the ECMWF's 148.0 CDDs.

Demand Implications (Natural Gas)

The competing regional forecasts carry different implications for natural gas demand and regional pricing.

• Heating Demand: Overall heating demand is present but not extreme for late April/early May. The key uncertainty is the regional distribution. An outcome closer to the GFS would support Midwest basis pricing relative to the East, while the ECMWF solution suggests stronger demand and price support in the premium Northeast markets.
• Cooling Demand: The emergence of consistent cooling load in the South will provide a floor for power burn, competing with the remaining heating demand for gas supply.
• Total Demand: The current outlook does not signal a strong bullish or bearish national weather event, but the regional volatility is a key factor to watch for basis trading and pipeline nominations.

Model Agreement & Caveats

Confidence in the 15-day forecast is moderate at best due to significant underlying volatility.

• Convergence: On a total weighted basis, the models appear to agree (GFS: 136.2 WHDDs, ECMWF: 141.5 WHDDs). However, the weighted_mean_abs_hdd_diff_by_day is 4.3, indicating notable daily differences are being masked by the cumulative totals.
• Forecast Instability: Confidence is significantly undermined by the run-over-run trends. The GFS added a substantial +12.1 weighted HDDs, while the ECMWF shed -8.2 weighted HDDs compared to the previous 12z cycle. This divergence suggests the atmospheric pattern, particularly in the 8-15 day period, is unstable and subject to further significant revisions.
• Source Limitations: This analysis is based on deterministic GFS and ECMWF runs provided by Open-Meteo. It does not incorporate ensemble guidance, which would offer a more complete picture of forecast probabilities and uncertainty.