GFS vs ECMWF Demand-Hub Outlook: 2026-06-01 00Z

Executive Summary

The 15-day outlook presents a significant model split, with the ECMWF forecasting a materially warmer and higher-demand period than the GFS. The ECMWF projects a total of 127.9 weighted Cooling Degree Days (CDDs), nearly 30% higher than the GFS's 98.6. This divergence is driven primarily by the Midwest and East, where the GFS sees cooler troughs suppressing demand while the ECMWF maintains warmer conditions. The GFS also trended significantly cooler run-over-run (-17.5 CDDs), widening the gap with a more stable ECMWF.

Hub-Level Weather

The primary driver of the national forecast divergence is the Midwest, specifically the high-weighted Midwest (Chicago) hub (35% weight). * Chicago: The ECMWF is substantially warmer, forecasting 107.7 cumulative CDDs versus just 36.4 from the GFS. The GFS also calls for 14.3 HDDs, indicating periods of below-normal temperatures, while the ECMWF sees only 1.3 HDDs. The largest temperature disagreements occur from June 7-9 and June 12-14.

Model disagreement is also notable in other key regions: * East (New York City): ECMWF is warmer, projecting 115.9 CDDs compared to the GFS's 78.4 CDDs. The GFS shows a significant cool-down around June 8-9 with over 14 combined HDDs, a period where the ECMWF remains mild. * South Central (Houston): In contrast to other hubs, the GFS is the hotter model here, forecasting 293.9 CDDs against the ECMWF's 226.5 CDDs. This suggests the GFS confines the strongest heat to the deep South while the ECMWF allows warmth to spread further north.

Demand Implications (Natural Gas)

The competing forecasts imply different outcomes for early June natural gas demand. * The ECMWF scenario points to robust cooling demand for power generation, particularly across the high-population centers of the Midwest and East. A 127.9 weighted CDD total would be considered supportive for prices, potentially tightening supply/demand balances and slowing the pace of storage injections. * The GFS scenario is significantly more bearish. Its projection of 98.6 weighted CDDs, coupled with 18.7 weighted HDDs, implies weak power burn for cooling. While the lingering heating demand provides some minor support, it does not offset the lost cooling load. * The latest run-over-run trend further supports a cautious stance. The GFS lost a substantial 17.5 weighted CDDs from its prior run, while the ECMWF was stable (+2.7 CDDs). This large GFS shift reduces confidence in its forecast for building heat.

Model Agreement & Caveats

Forecast confidence is moderate due to the clear model disagreement, reflected in a convergence score of 0.56. A score closer to zero indicates better agreement. * Divergence: The primary source of disagreement is the handling of upper-level troughs moving into the eastern half of the U.S. during the 6-15 day period. * Confidence: Given the significant bearish shift in the GFS and the relative stability of the ECMWF, there is a slight analytical lean toward the warmer ECMWF solution. However, the overall low model convergence warrants caution. * Source Limitations: This analysis is based on deterministic runs from Open-Meteo for a select group of demand hubs. It does not incorporate the full range of possibilities shown by ensemble systems. The demand weights are representative and may not perfectly align with specific utility service territories.