GFS vs ECMWF Demand-Hub Outlook: 2026-05-02 00Z

Executive Summary

Both GFS and ECMWF models trended significantly warmer in the latest cycle, reducing the 15-day heating demand outlook. The ECMWF remains the colder of the two solutions, forecasting 115.9 total weighted HDDs versus the GFS's 103.4. Major model disagreement exists for the Eastern U.S., where the GFS is substantially warmer and implies a quicker transition to cooling demand.

Hub-Level Weather

The national forecast is primarily driven by the high-weight demand centers in the Midwest and East, which are also the primary sources of model disagreement.

• East (New York City): This is the largest point of contention. The ECMWF is significantly colder, projecting 117.3 cumulative HDDs over the 15-day period, compared to just 80.0 HDDs from the GFS. The GFS introduces notable warmth around May 5-6 and again at the end of the period, while the ECMWF maintains a cooler pattern.
• Midwest (Chicago): While cumulative totals are nearly identical (GFS: 179.5 HDDs, ECMWF: 178.9 HDDs), there are significant timing differences. The GFS is much warmer from May 8-9, while the ECMWF is significantly warmer on May 11 and May 14. This indicates low confidence in the day-to-day pattern after the first week.
• South Central (Houston): Both models show a transition to cooling demand, but the GFS is more aggressive. It forecasts 144.1 cumulative CDDs, far exceeding the ECMWF's 117.4 CDDs.
• South (Atlanta): The GFS is also much warmer in the Southeast, calling for 70.8 cumulative CDDs against just 24.0 CDDs in the ECMWF.

Demand Implications (Natural Gas)

The outlook reflects a classic shoulder season pattern, with lingering heating demand in the north and emerging cooling demand in the south.

• Heating Demand (Res/Com): The ECMWF outlook implies more sustained residential and commercial heating demand, particularly in the high-consumption Eastern and Midwest markets. The GFS solution would see this demand fade more quickly after the first week. The run-over-run trend was decidedly bearish for heating demand, with both GFS (-17.9 WHDDs) and ECMWF (-20.2 WHDDs) shedding significant heating load from the prior forecast.
• Cooling Demand (Power Burn): The GFS is more bullish for early-season power burn, with 33.4 weighted CDDs versus the ECMWF's 25.4. This difference is driven by the GFS's warmer outlooks for Houston and Atlanta. The ECMWF's increase of 3.0 weighted CDDs run-over-run shows some of its lost heating load is being converted to cooling.

Model Agreement & Caveats

Confidence in the 15-day outlook is moderate to low due to material model differences, particularly beyond day 7.

• Convergence: The overall convergence score is 0.2528, indicating a notable level of disagreement between the models. The weighted mean absolute HDD difference per day is 2.96, confirming that the day-to-day variance is significant.
• Run-over-Run Shift: The large, coordinated shift warmer in both models (-17.9 GFS WHDDs, -20.2 ECMWF WHDDs) lends confidence to the overall trend, even if the specific daily details diverge.
• Open-Meteo Limitations: This analysis is based on point forecasts for a limited set of demand hubs, which serve as a proxy for the national picture. The demand weights are illustrative. The underlying models (GFS Seamless, ECMWF IFS 0.25°) are subject to standard forecast degradation in the extended range.