GFS vs ECMWF Demand-Hub Outlook: 00Z April 25, 2026

Executive Summary

The 15-day outlook indicates a transition to shoulder-season demand, with lingering heating load in the North and emerging cooling load in the South. The GFS model is forecasting stronger overall demand (192.4 total weighted degree days) compared to the ECMWF (175.8 TDDs), a difference driven almost entirely by the GFS's significantly hotter outlook for the South. Confidence in the forecast is low due to poor model agreement and a large warmer trend in the latest GFS run compared to its prior cycle.

Hub-Level Weather

The primary drivers of the national demand forecast are the Midwest and East, which account for a combined 65% of the demand weighting. Key differences exist across major hubs:

• South Central (Houston, 15% weight): This is the largest point of model disagreement. The GFS is substantially hotter, forecasting 177.7 cumulative CDDs versus just 116.3 CDDs from the ECMWF. The divergence grows significantly in the 6-15 day period, with the GFS showing sustained heat while the ECMWF brings in a cooler pattern.
• Midwest (Chicago, 35% weight): Both models forecast persistent heating demand. The GFS is colder overall, projecting 208.7 HDDs compared to the ECMWF's 191.1 HDDs. The largest differences appear in the Day 8-12 range.
• East (New York City, 30% weight): In contrast to the Midwest, the ECMWF is colder in the East, forecasting 201.0 HDDs versus the GFS's 190.7 HDDs.
• South (Atlanta, 10% weight): Similar to Houston, the GFS is much warmer, projecting 58.2 CDDs and 24.7 HDDs. The ECMWF is significantly cooler and shows more heating demand, with only 15.0 CDDs and 60.6 HDDs.

Demand Implications (Natural Gas)

The forecast reflects a seasonal decline in weather-driven natural gas demand. The national picture is dominated by heating degree days (159.9 weighted HDDs on GFS, 156.9 on ECMWF), but cooling demand is becoming a factor.

• Heating Demand: Lingering cool shots in the Midwest and Northeast will support modest residential/commercial heating demand, keeping it from disappearing entirely.
• Cooling (Power) Demand: The key divergence is in gas-for-power demand in the South. The GFS outlook implies a much stronger call on gas generation to meet air conditioning load, particularly in Texas, than the more moderate ECMWF forecast.
• Run-over-Run Shift: The latest GFS run trended significantly warmer, shedding 12.2 weighted HDDs compared to its previous cycle. This is a bearish shift, reducing near-term heating expectations. The ECMWF was more stable, adding a minor 2.1 weighted HDDs.

Model Agreement & Caveats

Overall confidence in this forecast should be low.

• Convergence: The model agreement is poor, reflected in a low convergence score of 0.22. A score closer to 1.0 would indicate strong agreement. The weighted mean absolute difference is a notable 3.5 HDDs per day between the models.
• Volatility: The large run-over-run change in the GFS highlights significant model volatility and uncertainty, particularly for the Day 6-15 period. Given the ECMWF's relative stability, its more moderate solution may be favored.
• Source Limitations: This analysis is based on a demand-weighted average of several key city hubs from Open-Meteo. It is an index for tracking demand trends and may not perfectly correlate with a full CONUS population-weighted degree day calculation.