GFS vs ECMWF Demand-Hub Outlook: 2026-05-26T00:00Z

Executive Summary

The 15-day outlook shows significant model disagreement on a regional basis, despite superficially similar national HDD totals. The GFS is notably warmer in the East and South, while the ECMWF is much warmer in the key Midwest hub. Confidence in the forecast is low, underscored by a very poor convergence score (0.38) and models trending in opposite directions versus their prior runs.

Hub-Level Weather

The national picture is driven by starkly opposing forecasts in the two largest demand hubs:

• Midwest (Chicago, 35% weight): The models show a major split. The ECMWF is significantly warmer, forecasting 103.9 cumulative CDDs vs the GFS's 55.1. Conversely, the GFS is much colder, calling for 28.6 HDDs compared to just 4.4 HDDs in the ECMWF. The divergence is most pronounced from May 28th through the end of the forecast period.
• East (New York City, 30% weight): The situation is reversed in the East. The GFS is much warmer, forecasting 72.8 cumulative CDDs vs the ECMWF's 22.1. The ECMWF sees a sustained cool period and projects 25.2 HDDs, while the GFS anticipates only 8.6 HDDs. This pattern is mirrored in Boston.
• South (Atlanta/Houston, 25% combined weight): Both models show consistent cooling demand, but the GFS is materially hotter, projecting 153.5 CDDs in Atlanta versus the ECMWF's 97.9.

Demand Implications (Natural Gas)

The shoulder season forecast presents a highly uncertain demand picture.

• GFS Scenario: Implies stronger-than-expected cooling demand (power burn) in the high-population centers of the East and South, partially offset by some late-season heating demand in the Midwest.
• ECMWF Scenario: Suggests the opposite, with robust early-summer cooling demand in the Midwest but significantly weaker power burn in the East, which instead sees persistent heating demand well into June.
• National View: The weighted national cumulative outlook is 92.4 CDDs (GFS) vs 84.5 CDDs (ECMWF), a relatively small difference that masks the extreme regional volatility. HDDs are nearly identical at 17.0 (GFS) and 18.1 (ECMWF).

Model Agreement & Caveats

Confidence in this forecast is low.

• Convergence: The model convergence score is 0.38, indicating substantial disagreement between the GFS and ECMWF solutions.
• Run-over-Run Trends: Confidence is further eroded by the models trending in opposite directions. The latest GFS run trended warmer (-4.3 weighted HDDs), while the ECMWF shifted significantly cooler, adding +6.0 weighted HDDs and removing -34.2 weighted CDDs compared to its prior cycle. This divergence suggests instability in the pattern recognition.
• Source Data: This analysis is based on raw, non-bias-corrected model data from Open-Meteo. Actual outcomes may vary.